Stop over-eating?

How do I stop over-eating? i have tried appetite suppressants and pills that make you feel full, but my problem is I dont have to be hungry to eat, and I have felt so full i am almost vomiting, but I still stuff food in my mouth. I have no will power unless Im around others, and even then i cant wait to get away from them so I can pig out. I try putting half the meal away and all that stuff, but as soon as I am done what I have, I go for the rest. I try not buying groceries except day by day, but I still end up going to the store again for more junkfood. HELP!!!