Ooh, ooh, I learned this in anatomy last week. Of course, do you think I can remember? No.

Anyway, you don't have to eat huge meals to gain weight. Just increase your caloric intake, but eat food more often. Now, does your stomach just stick out like everyone's does after eating, or do you look pregnant or something?
If it is abnormally large then go to your doctor, but if it is just what happens to the majority of us then I really don't know what to tell you. Sorry. I have the same problem and always have. You are quite thin also. I am surprised your doctor hasn't put you on a regimin to gain weight. Good luck.

Back to the anatomy thing....We were actually talking about the people in third world countries who are starving to death but have very large bellies. It is because of osmosis. You are lacking or do not have enough of something (cannot remember what) to break down the solutes in your blood. Such as proteins and whatnot. So anyway, it could be a thing that your doctor can help if it is serious. I am rambling, sorry.