Help! How can I shed inches FAST before my vacation?!?

My whole family will be going to Hawaii in about 3 weeks and I want to look really good when I hit the beaches. The thing is I cant seem to lose weight no matter what I do and my stomach is a MAJOR problem area! I'm sixteen years old and I just want to wear a bikini without feeling self conscious for once in my life! Can anyone give me some tips or a plan I could follow to lose some weight and get a nice flat stomach in 3 weeks!? Pleeeeeeease! :0 No stupid comments please! Anything you can tell me at all is appreciated! Thank you :)