Child, diet pills are not the way to go. They don't work, and most will have adverse effects on your body. I found that if you bike for 30-45 minutes every day, the pounds come off. I lost about 30 pounds in a month and a half with exercise and cutting down my calorie intake to 1200-1500. I had a cheat day every three to four days, where I put intake the normal amount of calories.
You may hear some pills that work like Alli, but those are not recommended for children. And, there is an embarrassment factor when using it... such as sporadic, uncontrollable anal discharge/diarrhea.
You're hurting your body more than you're helping it by using pills or going with bulimia/anorexia. Try a support group or support from friends and family if you need that push to do the exercise and right diet path. Best of luck.