Please someone help

So here is my problem
I never fill full.. Like I can eat and eat and eat and never be full. I can eat a 3 corse meal and still want to snack 10 minutes later. Why is this?! I've gained so much weight and I've got to do something about it! If I don't eat I get the WORST migraines, I've been put in the hospital because of it. Idk what to do! Someone please tell what this is, what can I do?!