Eat out of smaller dishes (seriously this works) and only eat when you're hungry, and when you eat eat good food! No bread or sugar. And drink a big cup of a hot beverage with every meal :) The best way to keep on a diet that I find is to forget the diet on the weekends and make them your cheat days :) And regular exercise of course :)
Looks like it took you about ten minutes to decide that at 14 years old and 200 lbs you think you're overweight. Having decided that, you want a fast way to lose 50 lbs by summer. Seriously, to do this right, and make it stick, see your doctor, get on a GOOD eating plan (I loathe to say "diet"!) and increase your exercise. Most of all, learn to accept your body image. You are sufficient as you are! But, being a teenager, I understand. Be sensible, go slow and smart. You must accept yourself before anyone else will.