Teenage Health and Fitness Question?

Ok I'm a fifteen year old girl and I have been trying to slim down to 140, I weight 153 at the moment and I'm 5'11. I cannot seem to kill my hunger pangs and its starting to show, atleast to me. I don't know how to stop them. I start out my day healthy and lunch I'm good but when I get home from school I mindlessly snack and then I end up eating too much at dinner time. Does anyone have any suggestions for my dilemma?