As far as I’ve heard what causes a stomach ulcer is too much acid and not enough mucus to protect the stomach lining. I have no idea about your case and I’m not a doctor, a bacteria that triggers an ulcer sounds possible but there’s lots of other potential triggers too.

In any case you really want to keep an eye on it, so it’s good that you’ve already been to a doctor. Making that first visit is always the hardest thing for me.