I don't know, but it sounds somewhat similiar to this thread.
http://www.medhelp.org/posts/Pain-Management/pain/show/1953906
If it isn't Im sure someone with a similiar problem might be able to help. Though going to the doctors again may be the best bet.
In my opinion when you say that it happens occasionally after eating, it sounds gas related. A Gastroenterologist can help you there.
I agree with Molleyrae, but understand your frustration. Is it after eating a certain food, or type of food? i wish i could help you. Gas pain can be very painful. Good luck.
shinty