(((Hugs)))
No input, but I know what you mean...many years ago my drs thought I was "just stressed" and strongly urged me to stop looking for work, and take time off from school (I'd just earned my AA and wanted to transfer, but couldn't imagine it with the pain).
Somehow a few weeks turned into a few years...and this is about 7 years later, gf for just over a year, and starting to heal. The concept of returning to work seems overwhelming, at least when you have that experience of your body physically baling out on you. Esp when there was no real treatment. (Other than avoiding the offending food. I don't know about you...but any meds they gave me made me so much worse!)

Since your GI believes you, perhaps you could get him to fill out the form? Slow recovery from debillitating illness caused by food sensitivities might be the best he comes up with though. And I have no idea how the disabilities office will accept that. Chronic fatigue seems a better bet.