What is the quickest, healthiest way to lose weight by summer? HELP?

I am 13 years old ( 170 lbs, 5 foot 3 in). I want to lose weight and be able to wear a bikini by the summertime for my trip to Nantucket. I have an unwanted desire to eat lots of very unhealthy foods and most the time I can't help it and don't realize i do it. Also, I am always busy. I have school from 6 to 4 Monday to Friday. I have Lacrosse Practice after school every Tuesday and Thursday. In lacrosse practice i don't get much of a workout as goalie. Also, on those days i get back at 6 or later and still have to do homework. On days without lacrosse I have lots of homework that usually lasts until about 6;00 pm. So, what do i do? Are there any major techniques/plans to help me? Any little things i can do throughout the day of school to help me? I want to look like this (http://images.olsen-twins-news.com/photo/large/13136fc351b8fca1a3efe12bd2e9ab95/audrina-patridge/audrina-patridge-in-bikini-for-bongo-spring-2011-campaign-olsen-twins-news-com-570x765.jpg) I look like this (http://www.babble.com/CS/blogs/famecrawler/2007/09/08-15/charlotte-church-bikini-pregnant.jpg) HELP ME PLEASE