Dear Amy, 

First of all, thank you for writing me this letter. I am sorry after hearing about your problems. Your first problem is about your weight. In my opinion, you should have a healthy diet and try to do some exercise, such as playing ball games and swimming. If you keep on doing these, I am sure you will become thinner and healthier. Your next problem is about your English schoolwork. I think you are afraid of learning English so you get bad grades in English tests. I suggest that you should give yourself more chances to listen to and learn English, such as watching TV programs in English. If you keep on watching them, you will have great improvement in English. 

Hope my advice works.

Mrs. Smith