Suggest Medication For Pain In The Right Side Of The Stomach

My bf has been having pains on his right side stomach, his pain's sometimes occurs around the front side of his stomach and also his back, becuase of this pain, he often feels like he is stuffed and cannot eat, also when he does not eat he feels better but then feels hungry, now as his gf I have noticed that he does not eat enough to say that he is over eatting, if anything he may be under eatting, but because of his pain he always feels stuff for the majority of the time, now there are days where he will eat normal amount of food ( 3 regular meals aday) and then start to have his pains and such occur, and there are days that he will over eat and yet again still have these pains.

I wonder if this has more so to do with poor eatting habits, but I'm also leaning towards there being something more so wrong only because he has had weeks of eatting normal (3 meals aday and sometimes a few snacks) Also he is pretty healthy and works out occasionally. However I'm curious as whether or not this may be caused from over stressing, he has periods of times where he does seem to over worry, and from personal experience know that can cause health issues to, but its usually a one week or 2 weeks thing. Is there anything you can tell me?