You probably don't want to drastically ramp up the fibre level in the diet, though slowly increasing it would be an idea. You need a mix of soluble fibre (as in fruit) and insoluble (as in grain).

Probiotics (live yogurt) might help. So might supplementary digestive enzymes like bromelain, and betaine hydrochloride (ups the level of hydrochloric acid in the stomach) - the idea is that if your stomach does its thing properly, there will be less half-digested food to irritate your intestine.

Chlordiazepoxide is a seriously addictive drug. Maybe okay as a one-off for acute episodes but not something you'd want to take day after day.