Good points by Gina. I am wondering what kind of doctor you are seeing? It is kind of typical to try different doses to see how they work. For a doctor to say he is on an adequate dose for his weight - seems to me like he doesn't want to take the time to figure out what is going on.
Since you haven't said how old he is or what meds he is on its hard to say much more.
I do know that meds alone are not the answer. If the only support a child is getting is meds, he very easily could start having more problems as he progresses though school. Is he is special education where he can get more help. Do you know how to help him effectively study at home? These things can make huge differences! I suggest you buy the book, "The ADD/ ADHD Answer book," by Susan Ashley. You will find a lot of things that you can do to help him, and also make the school help him.
Best wishes.
Yes, it is possible that the medication is making things worse. I have had doctors tell me that I will just have to stay on medication for various conditions for the rest of my life. While taking them though, I was worse than when I wasn't taking them.
Talk to the doctor about your concerns with the medicine. Let him/her know exactly what your child is like on and off the medicine. The doctors can make recommendations, but they only see your child for a few minutes every once in awhile. You are the one who has the daily interaction. In the end, you have to do what you feel is best for your child. If this doctor is not willing to work with you on finding a solution, then find another doctor.