They're still running tests. The doctors have suggested the following diets:
FODMAP
Celiac diet (gluten free diet)
Paleo diet
SIBO diet
TMAU diet--hasn't been suggested yet but most doctors haven't heard of it.
The gastro said that these diets take MONTHS to work. What we eat is the key but it's trying to find the right diet for what we have. (So far, all the tests have been negative.)
One thing that many of these diets seem to have in common, avoid flour.