Consistent upset stomach?

Okay well, in mid December of last year I had gotten a stomach virus and was VERY sick. Ever since, I have been getting an upset stomach and occasional diarrhea along with it. It usually starts as some abnormal pressure in my lower abdomen(lower stomach, not like menstrual cramps) that makes me feel nauseous for a minute. I also get that strange bubbling in the same area(I usually get this when my stomach is upset). This has happened about 3 or 4 times since my stomach virus. It usually occurs near the time of my period but I don't believe it has anything to do with that. This is very embarring for me and I'm starting to worry. I've tried Pepto Bismal and some other anti-acid relievers but they don't do a thing. I'm only 15 and I'd rather not consult my parents or my doctor about it unless it becomes a major problem. I eat yogurt practically every day after school so I really don't know what's wrong. Can someone help me?