It's a crisp, sunny winter's morning and Lucilla Paull is at the park with her sons William, six, and Ben, five. The boys are racing around playing football, and Lucilla – a keen sportswoman who played rugby for her university – would love nothing more than to be running around the grass with them. Instead, she's watching from the sidelines in a wheelchair. "If there was ever a time in my life when I wanted to be able to run around, it's now," she says.

It's because Lucilla is a mother that she is in a wheelchair. She has a condition called symphysis pubis dysfunction (SPD), which affects the alignment of the pelvic joints and is a common complication of pregnancy. Most women recover or aren't much troubled by it after the birth, but for a tiny minority, such as Lucilla, the effects are extreme and peculiarly cruel.

She is, she confesses, still shocked that her pregnancies could have done this to her body. "I couldn't have imagined that having babies would leave me disabled," she says. "But that's what happened. I'm 38, but my body feels like the body of an old woman. I'm registered disabled, on very strong drugs and, increasingly, I have to use a wheelchair, even round the house. A few days ago I fell over in the yard and I didn't have my mobile phone with me – I was completely stuck, I couldn't get up. It was about 15 minutes before my husband James and the boys found me. I just had to lie there, outside, on a freezing cold day."

In 2004, when Lucilla first got pregnant, soon after her marriage to James, she had never had back trouble or pelvic pain of any kind. "I'd hardly had a day's illness in my life," she says.

The pregnancy was straightforward, but Lucilla started to suffer from hip pain, often finding herself limping as she got off the train from her home in Bedford to walk to the London bank where she worked. "It was really uncomfortable, and in the end the obstetrician suggested inducing the baby 10 days early," she says. All was fine: William's delivery was easy, and within a few days Lucilla's pelvic pain had disappeared.

But nine months later, when Lucilla got pregnant for a second time, the very first indication that she had conceived was a familiar ache in her pelvis. "I didn't even need to do a pregnancy test – the pain was back," she says. "This time, it was worse than with William – by three months I was in a wheelchair, which was extremely difficult as I had a baby to look after and a husband working full-time in London.

"The pain was so bad that I barely left the house for six months and was even admitted to hospital for three weeks leading up to Ben's birth. I'm a fiercely independent person, and hate having to rely on others, but I had no choice, and my family and friends pitched in to help. It was a truly horrible time, being in constant pain, but at least I knew there was an end-date. The baby was due in mid-March, and I knew I'd be fine right after that."

Only she wasn't. "Ben's birth, like William's, was induced – this time six weeks ahead. To help the baby's lungs, I was given steroids and advised that a normal delivery would be better for him. So I went ahead, but the pain was dreadful. It wasn't just labour, I could tell that – it was my pelvis. Once Ben had been taken to special care, I sobbed and sobbed." She now knew, she says, that she couldn't go through pregnancy again. "I was advised not to have a third child so, when Ben was a few months old I was sterilised, despite being only 32," she says.

But the pain, which doctors had been so confident would disappear after Ben's birth, carried on. "What made it worse was that the doctors simply wouldn't believe what I was telling them – they said I couldn't be in all that much pain. It was utterly depressing and frustrating: I had two small children to look after, my life was being battered by pain and yet the physicians didn't believe me."

Eventually, she found a sympathetic consultant who did an exploratory operation and made a diagnosis: the SPD had led to disc problems further up Lucilla's spine. "The consultant told me I now had a very severe back problem that needed surgery."

At first, the operation seemed to have worked. "I was home the next day and having been unable to walk half a mile, I was walking five miles within 10 days of getting out of hospital. It felt like a miracle. I thought, this is the beginning of the rest of my life. I'm going to be an ordinary mum; I'm going to be able to enjoy my boys. I could go horse-riding again and that has always been my passion."

Then, gradually, the pain started to return. "I couldn't believe it," she says. "I went back to hospital and had more tests. They showed the discs had disintegrated further. I needed another operation, in which two or three of my discs would be fused – and, according to the doctor, I would probably face further operations later in my life."

As we talk, Lucilla is lying on her sitting room sofa – the only position, she says, in which she can be anything like comfortable. She had to give up her job in the City: "Commuting was impossible and I can't even sit at a dinner table, let alone a desk." Instead, she works from her bed or the sofa, running recommendedfamilyholidays.com – a website advertising family-friendly holidays in Britain, France, Ireland and Cyprus. "Setting up the business has been a lifeline for me because it means that even if I'm too ill to get dressed, I've got work to focus on when the boys are at school, and that helps enormously.

"There's a need for this sort of word-of-mouth website, and I feel I'm doing something really useful – and thinking about holidays transports me far away from my sofa ... "

Lucilla faces another exploratory operation next month and then expects to have to wait several months for the disc-fusion surgery. "It's not easy," she says. "I have some very bleak days. I'm having to dose myself up with morphine, I can't drive long distances and I never get a proper night's sleep. Walking to the park is out of the question, let alone playing with the children when we get there."

Lucilla says her condition has put a lot of pressure on her marriage. "I think it has been worse for James than for me. He never knows how I'm going to be when he walks through the door. The children have had a different childhood than the one they might have had: they are a lot more independent than children of five and six usually are. They get themselves ready for school and get their own breakfast. They get hot water bottles for me and bring me what I need. "They love racing around, but they know I can't do that, so we play a lot of board games and other games I can join in with, like Simon Says, their current favourite. They are such fabulous, caring little boys."

Lucilla is adamant that she doesn't want anyone's pity and says the reason she is sharing her story is to alert other women to her situation so they don't have to go through the same thing. "Lucilla is right – no mother needs to be in the position she is in," says Sarah Fishburn of the awareness group the Pelvic Partnership. "Pelvic problems in pregnancy are treatable, and they tend to respond very well to good physiotherapy. The problem is that midwives and obstetricians tend to assume that things will get better after delivery, and though many cases do, there's always a small number of cases where symptoms don't improve. But the people you see when you're pregnant – midwives and obstetricians – are not the same people who would see a woman like Lucilla further down the line, so the message isn't getting through to those caring for pregnant women that these problems have to be taken seriously, not ignored, and referred to properly qualified physiotherapists.

"The key message for women is: if you've got joint pains in pregnancy, don't ignore them – and don't let a healthcare professional tell you it's something you've got to just put up with. You don't. These pains are not normal in pregnancy – they are symptoms of a problem that needs treatment."

Lucilla says she tries not to dwell on what might have been. "I know that if I hadn't had two pregnancies – or if I'd received the proper help I needed during them – I'd still be moving around normally and still doing the job I loved. But for me regrets aren't possible because my children are fantastic and despite everything I'd still say that, because of them and James, this is the happiest time of my life. I'm determined to keep it that way, too – it would be too easy to spiral into depression, but I have to keep remembering how important it is to stay positive for the boys' sake and for James, as well as for me."

Information: Pelvicpartnership.org.uk, helpline 01235 820921