You need to start eating properly. I'm not gonna go into small details, but seeing how you need a quick solution I can throw in a couple of pointers at ya:
1) realize that your body is still growing, and by "dieting" the way you're doing now you will most likely cripple yourself (e.G. Inhibit your growth)
2) calculate your bmi (body mass index). This will give you a rough approximation of how much you should weight for your age and body size
3) measure your eer (estimated energy requirement). This will tell you how many calories a day you should consume to keep your current weight consistent. If you consume less than that, you lose weight. More than that, you gain weight.
4) do an extensive research on macro and micro nutrients. You must understand why you have to eat food in the first place (i.E. Why and what kind of food is important for your body).
5) always read nutritional table on the back of meal packages which you buy. Things you have to avoid at all costs are sugars (in carbohydrate section), enriched flour, anything "processed" (in ingredients section), saturated and trans fats (in fats section). In other words, you have to stay away from about 90% of packaged food sold in stores. Also, the trick is to consume as few calories as possible while eating as much food as possible. You can achieve this by eating foods rich in protein, complex carbs, and healthy fats.
6) never try to lose weight by dehydrating yourself! Drink plenty of water.
7) lose weight gradually by doing cardio exercises. Max 3-4 lbs a week. Make sure you don't exceed your target heart rate by a lot, lest you want to lose "weight" while remaining fat (i.E. Burn muscles)
8) it takes a long time, months, definitely not weeks, to lose extra weight, even if you create caloric deficit by eating less than your eer and running on a treadmill every day! You won"t be able to slim down before the school starts! So shoot for the spring graduation and next summer.
9) last but not least. When you're in college, take nutritions 101 class - not for an easy credit, but to absorb as much knowledge as you possibly can.