I want a bikini body by mid may!?

So at the moment I'm 16 yrs old 5' 5" and about 135 lbs :( i would like to lose 15 to 20 lbs because I really want to look and feel good in a bikini this summer! I need a straightforward easy to stick to plan that will help me acheive this. Im going to be getting up at around 6:30 am to start doing things like situps and pushups and stuff like that, and for cardio i have and elliptical and i can also run outside or jumprope. Any tips for staying on track and are helpful and much appreciated! So what is the best way to go about the diet portion? and is this an achievable goal? Also what are good exercises to do for a flat ant toned tummy and also for my sides