Suggest treatment for constipation and sore stomach after following a brat diet and self medication post a laparoscopic Nissen fundoplication

Question: Symptoms: constipation followed by very explosive diarrhea (mixed with normal bowl movements) and excessive gas from mouth and rectum as well as intermittent stomach ache below sternum. Time period: Monday, constipation followed by explosive diarrhea in sleep. Tuesday and Wednesday morning, fairly normal BM plus persistent gas and some diarrhea. Self medication: 3 doses of donnatal -1 every 12 hrs. Prior history: diverticulosis and gr'litis and had lap nissen fundoplication in January so cannort vomit. Today, through a nurse, a general prac MD friend recommend gas-x plus a brat diet and loperamide after diarrhea if it persists. Gas-x was about 50% successful. I took one dose of loperamide (unused 2yr old Rx) around 4 pm but wonder if this is the source of stomach pain if what's in stomach cannot vomit or exit through BM. I'm not a physician but I would think that donnatal would be better because right now, after overeating brat food, I'm unpleasantly, temporarily constipated with a sore stomach. What would be your call on this for relief.