How do I do it?

Rikki
Before I ever got pregnant I weighed a healthy 110lbs. I got pregagnt with my first and continued my regular exercise and never gained any weight,leaving the hospital after having him at 100lbs. With my second I gained 65lbs. And got pregnant 2 months after I had him and gained 10 lbs from her. I now weigh 165lb. I need to lose 55lbs and would love to before my 21st bday. How can I lose that much wait in only 3 months? Any ideas. No ride comments please. !!