Bedtime back pain
Q For the past six months, I've found that lying in bed all night gives me an ache towards the base of my spine, in the middle of my pelvis, and sometimes in my hip joints as well. This wakes me early every day and I have to get up because, even if I'm still sleepy, my back is too uncomfortable if I continue to lie down. Once I've got up and moved around for just a few minutes, the discomfort vanishes.

At first, I wondered whether my bed might be at fault, but the mattress is fairly new and well made.

I don't know whether it's relevant, but I'm a 57-year-old woman, on HRT, and more than a stone overweight. I'm ashamed to admit that I sit in front of my computer and don't do much exercise, although I walk for approximately 20 minutes every day.

A In all likelihood, you have what is known as mechanical low back pain, caused by wear and tear rather than any underlying disease process. If that is the case, you will be advised to take anti-inflammatory pain killers when the pain is bad, or perhaps co-proxamol to help you sleep and give pain relief.

Manipulation by an osteopath, chiropractor or physiotherapist may speed up recovery. In the longer term, losing excess weight, keeping as active as possible and attending a back clinic to learn how to do back exercises to prevent recurrence is the key. Given the duration, severity and type of your pain, I'd want to do some blood tests and possibly x-rays to ensure there is no other underlying problem.

Water births
Q I'm expecting my first baby next January and am very keen to have a water birth. My brother-in-law, who works as a gynaecologist in the States, said that he thinks I'm mad and would be endangering the baby. What's your advice?

A Far be it for me, a British GP, to disagree with an American specialist but recent evidence suggests that if you're enjoying a normal pregnancy and are considered at low risk of any complications, water births are as safe as any "normal" method. You'll be in a minority - only 2,000 deliveries a year, or just over half a per cent of all deliveries in England and Wales are water births. Over the two-year study period, no deaths were directly attributable to having been born in water among the 4032 waterbirths. This is one to discuss with your midwife or obstetrician but it would seem that provided you remain at low risk of complications, water birth should be a safe option for you. Your brother-in-law may want to look at the study in the British Medical Journal (BMJ 1999;319:438-7).

Lump worry
Q I've got two firm lumps under the skin of my forearm. They seem to be getting bigger and when I straighten my forearm, you can see their outline through my skin. They don't hurt or itch but my girlfriend says I should definitely get them removed. What do you think?

A Diagnosing lumps via a newspaper column is asking for trouble, so you do need to get them checked out by a GP. Having said that, they do sound like fat lumps, or lipomas. I'm the proud possessor of a couple myself and have become quite fond of them. They don't become cancerous and can be left alone. They do tend to grow and can occasionally cause some discomfort if, for instance, they press on a nerve. If you want to have them removed, ask your GP; some GPs do it themselves, others will refer you to a local surgeon. They inject some local anaesthetic, make a cut across the lump and carefully remove the whole lump. Personally, I'm hanging on to mine.

Vaginal soreness
Q Last year I developed a condition whereby the inside and outside of my vagina became very sore and red. There was little or no discharge and no itch. Over a period of several weeks I was swabbed for thrush and other bacteria and although all swabs were clear, I was prescribed Canesten several times. This appeared to make the condition worse and it eventually went away about four months later. I do not take bubble baths, use non-biological washing powder, wear cotton knickers and do not wear tights or tight trousers.

A You've either got an infection or an allergy. You've certainly done all the right things. A sore, red vagina with little or no discharge is often caused by a bacteria of the streptococcal family. Swabs don't always grow the bacteria and you may want to try a course of penicillin by mouth on spec.

The best place to be checked out for vaginal infections is a sexually transmitted diseases (STD) clinic; not because that's what you've got, but because they have walk-in clinics with no waiting time and can do all the tests on the spot. Your local hospital is bound to have an STD clinic, though you may want to discuss it first with your GP.

The other possibility is an allergy, though it sounds as though you're avoiding all the common allergens. Did the symptoms coincide with starting to use condoms or the cap - perhaps you're allergic to rubber or the spermicide? You could try taking an antihistamine by mouth; if it helps, it supports the idea that it's an allergic reaction. You could be referred for allergy testing if the problem continues.

Word of mouth
Q I had two wisdom teeth removed from the left side about 15 years ago. Since then, I have been suffering from muscle spasms, aching and tiredness in my jaw on that side, a minor inconvenience at first, but it gets progressively worse. The spasms cause deep bites in my tongue when it gets in the way, and besides the continual dull ache, I am increasingly worried that I may bite it off. I have visited GPs and dentists but they have been unable to suggest a cause. I went to an osteopath five years ago who thought it might be due to nerve damage, but couldn't offer any remedy. Any ideas?

A Last time I answered a question in this column about mouth ulcers, I received an irate letter from a dentist about uppity doctors who comment on oral problems; fair enough, given that dental students spend five years studying mouths, whereas medical students spend more like five hours on the subject. So, to try to answer your question, I chatted to an oral surgeon at a dental hospital.

The upshot was that it sounds as though the removal of your wisdom teeth may have contributed to pain round the jaw joint with resulting muscle spasm. Nerve damage can occur during wisdom teeth removal but tends to cause loss of sensation to the lip, chin and tongue on that side, rather than spasm.

The oral surgeon thought it was unusual for the spasm to be so severe as to make you bite your tongue. She did say that she has never heard of anyone biting their tongue off! The treatment would usually involve making you a bite guard to wear over your bottom or top teeth at night to stop you clenching or grinding your teeth, which would aggravate the pain and spasm. If this doesn't work, they usually prescribe a three-month course of low-dose anti-depressants to take at night. You should see your dentist who may refer you on to an oral surgeon.

• These answers are intended to be as accurate and full as possible, but should never be used as a substitute for visiting a doctor and seeking medical help.

If you have a question for Dr Robinson, email drann@dircon.co.uk or write to her c/o The Health Editor, The Guardian, 119 Farringdon Road, London EC1R 3ER. She regrets that she cannot enter into personal correspondence.