There is just no way to really tell. I would recommend seeing your doctor for it. It really could be a lot of things. Off the top of my head I'm thinking ulcer, but it could be indigestion or GERD.
I hope you get it checked out and everything's okay.
I agree with Jaded Sweetheart. There's just way too many things possible. How often do you get it? I it related to anything you eat or drink? How long does it last when you get it?
I've been haveing the problem for over a year, and it lasts about half an hour to an hour. And i'm not sure how often I get it I don't really have a good memory either.