I had an idea in the middle of the night AJ. Many "sensitive stomachs' from stress come with the diagnosis of IBS with diarrhea. IBS stands for irritable bowel syndrome. One of the most effective over the counter treatments, and often recommended by drs, is insoluble fiber. The best of these is wheat bran which can be bought easily and added to baked goods, cereal, smoothies, etc. Depending on the person's size and symptoms most drs recommend 20 to 35 grams of wheat bran a day. It only takes 3 or 4 days to see a marked improvement in symptoms. Wheat bran also has the advantage of having significant levels of many vitamins and minerals.
One of the best foods available for wheat bran is Post Shredded Wheat. It takes about 3 cups to get enough insoluble fiber and the down side of that is you will be also getting a lot more carbs too. I buy and use wheat bran from Amazon and it has helped my digestive issues a lot. What have you got to lose?