Don't worry! Everyone has their own metabolism levels and diets. I wouldn't go with the cleansing diet. It might seem like the right way to go, but try finding something that works for you first. Your perfect just the way you are and don't let peer pressure get to you if that's what made you decide to lose weight. Don't rush it either, it will happen, just exercise and eat healthy and *regularly*
If this is coming from a Freshman girl in high school, it means something
That might not be possible to do in a healthy manner. All you can do is cut most carbs, eat more protein and work out regularly. Doing it any other way than with a change in lifestyle and eating habits usually doesn't stick and you put it right back on. Good luck!