Right now, life isn’t so bad for Robert Wells. “I get the odd uncomfortable day,” says the 48-year-old cartoonist. “But it’s not a major issue. You won’t catch me riding a bike, though.”

As recounted in his commendably – almost excruciatingly – honest new graphic novel, Wells has been experiencing chronic health problems since 1990, most notably a persistently upset stomach and a perennially aching right testicle. Which partly explains why his book is called Back, Sack & Crack (& Brain). If this sounds funny, he’s OK with that. “The main reason I wanted to do the book was because I could see quite a lot of opportunities for humour.”

These embarrassing ailments have had a debilitating impact, though. Decades of constant pain, anxiety about getting “caught short” in public and indifferent – sometimes hostile – medical professionals have all contributed to a deterioration in his mental health. Even though recent years have seen a drop in his physical suffering, Wells continues to take antidepressants.

At the height of his troubles, he also developed agoraphobia and panic attacks. “I wouldn’t go into shops that had sliding doors,” he says, “in case they got stuck and I couldn’t get out again. It was that bad. I still don’t go out on my own all that often.”

Then there’s the intermittent back pain, which has prevented him from holding down a regular job for years. When he began his graphic novel in 2014, he was claiming incapacity benefit, but that was stopped following an Atos assessment. “My health problems have held me back in life a lot,” he says. “They still do.”

The book follows Wells, who is from Ashford in Kent, through a series of encounters with the NHS, as doctors misdiagnose his ailments (he’s erroneously operated on for a twisted testicle in 1997), express scepticism about his claims, or simply fail to take him seriously. “I’m quite oversensitive that everyone will now assume I’m anti-NHS,” he says. “But I’m not. I think, in part, I just got unlucky. My feeling is that I saw a couple of bad doctors early on, and their negative notes followed me to every other appointment.”

It’s a dispiriting journey, as Wells’s hope for a proper diagnosis and treatment is gradually ground away. “That’s one of the points of the book. Most people seem to go through life thinking that, unless it’s something terminal, their doctor can sort it out. But that’s not the case, is it?”

There’s much more to his story than just “sore balls”, he says. “I think there are a lot of people who are ill and not living their lives in full because of it. But they’re not really considered ill by the state. Many of the doctors I saw were surprised I wasn’t delighted to be told they couldn’t find anything wrong. But I felt terrible. There was a big part of me that would have preferred it if they had, because at least they might have been able to do something about it.”

One revealing incident sees him being referred for a mental health assessment. Afterwards, he is accused of being a “bloody liar” by his GP. “I honestly think she assumed I was pretending to be ill to get benefits,” he says. The doctor then presents him with the psychiatrist’s findings: “Although Robert is an extremely anxious young man, I believe that further psychiatric treatment would only encourage him in the belief that he is ill.”

Wells elaborates: “I remember telling health professionals, ‘This is stopping me going out.’ And the doctors would say, ‘This is stopping you going out?!’ As if it was unbelievable – that a little thing like testicle pain could affect you so badly. I certainly recall saying to a GP, ‘I’ve become very agoraphobic’, and them replying, ‘Well, you made it here all right today.’”

Throughout the book, Wells is admirably frank in depicting himself in an array of demeaning, trousers-down situations. He tries to alleviate stomach pain through alcohol, spends eight years only eating raw carrots for breakfast, and masturbates in an attempt to ease tightness in his groin.

Nonetheless, he says: “I am embarrassed about this stuff, particularly the bowel problems, for some reason. But what I wanted to say was, ‘I don’t see why I should be.’ Why should I be embarrassed for being ill?”

Wells doesn’t offer any resolution in terms of what has actually been wrong with him all these years. “It’s, ‘I don’t know what the fuck happened, don’t ask me why I ate raw carrots.’ But it has been quite cathartic, writing and drawing it.”

At the moment, the worst of his ailments have gone into abeyance – for no apparent reason. “I can live with not knowing, although there’s a part of me that’s hoping someone will now get in touch and say, ‘This is what you’ve got.’”

There’s also the dream that Back, Sack & Crack (& Brain) will rescue him from the limbo of not feeling well enough to work, while not being definably ill according to social services. “Hopefully, I’ll become a multi-millionaire off the sales. If the only way I can get out of this mess is by becoming the public face of achy balls and irritable bowel syndrome, I’m prepared to sink to that level.”

• Back, Sack & Crack (& Brain) is published by Little, Brown on 29 June. Order it from the Guardian Bookshop