Help!! I feel hungry and nauseous after eating?

Okay, I am 23 years old and am about 80 pounds over weight. I'm constantly trying to loose weight..and I always feel like its a struggle. Sometimes i'll loose and then sometimes I don't. I am not sure what is wrong with me. This is a pretty random thing.. i'll eat and about an hour or so after eating i get this starving/nauseous feeling. Like i haven't eaten in days... Its a random thing, but it happens alot. I can't tell what is causing it. And i don't think it is what I am eating, because i've noticed it happen after eating fast food...home cooked meals.. dairy.. fruits..veggies etc.. i can't narrow anything down in particular. 95% of the time i'm trying to eat healthy anyway.. to loose weight. and i do eat 3-4 meals a day. So I don't get it.. I brought it up to my doc once.. he just brushed it off. I'm at a loss... any ideas?