Probiotics an expensive fraud, IMO, but I'm glad if they help anyone. GPs are amazingly helpless. I'm on Metamucil, Olestyr, Dexilant and Align and it's just all useless. Still require supplements of Immodium up to 8x a day.
Tests, incl colonoscopy/enteroscopy revealed nothing. I'm not stressed, either. No more than anyone else, probably less than most. Love my life most days.
New theory: Feels like auto-immune response. Body treating all the sand, Dexilant, etc. like they are parasites such that I am now producing battery acid instead of mere stomach acid to fight them. That's what it feels like.
So far, respirologist was the most useful. Made the asthma-IBS connection and actually solved the asthma problem. Does your son have asthma? If so, consult respirologist. NOT an allergist but a respirologist.