If celiac, Crohn’s and other problems have been ruled out then lactose intolerance and IBS are the possibilities. Gas
in stomach, burping, diarrhea all go in favor of IBS. Pancreatic enzyme disorders, liver dysfunction, HIV, cancer of the gut, and infections by parasites other than giardia can all cause persisting diarrhea. Lyme and lupus are other possibilities that present this way. Please discuss this with your doctor (GI doctor). Take care!