I'm not a doctor, and certainly you should consult yours, but I have never had a medication I've done well with, that later caused me problems. I'd suspect it's something else. I've taken Singular for a long time, and I've got a very sensitive stomach. I get gastritis very easily--I've never had a stomach problem that I could relate to Singular. When I get a gastritis flare up, though, I eliminate as many meds as possible until I clear it up.
Good luck with your son!