Quick weight loss help? ?

Right now, I am 15. I am 5'7 and around 160. I have 3 weeks till my school starts, and I really want to lose weight and slim down. I have a bit of an obsession with junk food and I know that if I want to lose weight im going to need to cut that out. And start excercising alot more. Basically what im asking, is there any chance that if I stay true to this routine, is there any chance that there will be noticeable weight loss with in 3 weeks? It seems pretty far fetched to me.