Dear Jack,
I am sorry to hear that you often feel tired. Let me give you some advice. First you should eat breakfast every morning.Eating breakfast can help you study well.Then you should do more exercise after school. Doing exercise can make you keep healthy. It is also very important to sleep eight or nine hours a night.A good sleep can make you feel good and study well in the day. Try to have a healthy lifestyle and then you can study well.
Yours,
WangPeng