I've experienced many of your symptoms, and for me it's down to food intolerances , lots of them. I have been tested for celiac, and all other allergies, all negative, but I know I cannot eat many foods because of the very reactions of which you have described.
However, I believe my own intolerances are the result of something else going on in my body which has yet to be diagnosed. I was diagnosed (via the new Video cam/ pill cam last month) with a Ulcer of the duodenum, diverticulitis of the jejulem ( a rare condition apparently) , and a narrowing of a vein that supplies my small intestine. Having surgery/enteroscopy 8th Nov for a better look.
Despite these findings, my Dr thinks they would not cause my worst symptom ...5 years of chronic diahorrea, he too says its stress. Yeah right!!! But I know my diahorrea is related to my food intolerances .