Drink lots and lots of water, that will fill you up. Over eating is natural, because over the centuries food has been scarce for humans, so we eat as much as we can when we can, its practically in our genes. But food is of abundance now (not all countries I know) and its processed.
Well, you have to look for the reason, because when you find it, you can stop.
At your age, it could be PMS. It could also be what you are eating. High fructose corn syrup, msg, aspartame among other things increase your appetite substantially and cause other problems.
I have this theory that some people are psychologically addicted to putting stuff in their mouth. Maybe this stems from over use of soothers as a child. I really don't know; but, if this is the case with you; then try to find something that either: a) cures your psychological addiction; or, b) has no calories.
I am the exact same way but i hardly eat a single thing that is unhealthy for me. Even when I feel full I ust want to eat more. I dont gain any weight besides the weight im supposed to during pregnancy.