Fasting really isn't a good weight-loss method. Fasting tells your body that food is scarce, so when you start eating again the body will hold on to whatever you eat ever so much harder, making you prone to quickly gain whatever it was that you managed to lose. The trick behind a good diet is that it will keep your body going, while still restricting your calorie intake enough for you to lose weight.
On top of that your body(and your mood) can get int all kinds of upsets when you deny it the fuel that it needs to function properly. And if you're the same 15-year old who's written similar posts recently - well, fasting is questionable enough for adults, and for someone who's still growing it's outright unsuitable.