Sleep. Eat healthy. If you use chemicals like sugar, caffeine, and the like to stay awake, you will just hurt your body. Get enough rest every night, and stay away from sugar, especially soda. Drink water. Milk is good too. Make sure you get enough vegetables. A salad a day is a good habit, and can help keep you from getting tired in the afternoon.
Again: relying on sugar and chemicals will make you a) fat b) sick c) maybe diabetic. And after your body gets used to them, you will be tired again, like you see happening now.
Oh, and stick to beer. Liquor is much worse for you, and when mixed with sugary substances is several times more effective at killing brain cells. I mean, when you turn 21.
