Benay, my dog had gi problems. I can't say his issues are the same as yours but I did find a diet that seems to work for him. When the vet was useless.

5 food types are totally eliminated, and added probiotics, digestive enzymes and tumeric at each meal.

No dairy,
no glutin.
No solanine, like potatoes, tomatoes, eggplant. It's a very large list so look up a complete list.

I'm trying to find my notebook with the complete list.

Took many many weeks, like two months.