It depends on your gastrointestinal issues. The First step is access your symptoms with the help of gastroenterologist. He Will probably ask you to have two tests done: colonoscopy and endoscopy.
Then, as soon as they get results they will give you certain meds to help you. But if you would like to get started there are a few things you can start doing to reduce discomfort.
If your stomach hurts (ornif you have heartburn) avoid carbonated drinks, condiments (ketchup, mustard, etc), Peppers, processed foods in general, coffee, acid foods (pineapple .lemon , organge etc).
If you have intestinal issues (dont go to the bathroom as often as you should): you can eat papayas, eat plums (also place plums inside water in a Cup and leave overnight, in the morning drink the water and eat the plums)...also eat lots of fiber...it should help you :)
I am saying from experience as I have suffered all my life with related issues.