Have you kept a food diary?  When I first got diagnosed with Crohn's I kept a diary for a few months to figure out what triggered symptoms.  I eliminated everything but pretty bland stuff and then added foods one by one.  It was really annoying, but it had great and surprising results.  I had been drinking Coke for years but found it (and most caramel sodas) create undesirable side effects.    You should check out with some different kinds of doctors, too, I know you say you've tried a lot already, but maybe it will help whichever doctors you see if you can bring some dietary history or info with you too.