I agree that it sounds like depression. I think you might be feeling a lot of stress over doing well and you're sort of falling apart as a result. I would go back to the doctor and say that you are not doing better--in fact, things are getting worse. Some people do need medicine to help them. Also, is there someone at your school, like a counselor or a therapist, you can talk to?

I guess it's possible you have some ADD, but you would need more testing with a professional to confirm it. However, the fact that you have done so well before makes me wonder about that diagnosis.

Let us know how things are going!