I don't remember now which antibiotic it was specifically. Maybe because the idea that the trigger might've been the antibiotic arose much later. At that time, I still had blind faith in doctors! Even when my own dad, himself a doctor, was telling me something like, "if you start taking pills you'll need to take other pills later to cure the things caused by the former pills"!

But I think it was to kill the helicobacter pylori. Itself a questioned, if not debunked, practice currently.