I haven't had a cycle in........?

Go back to the doctor and ask them what it is that is causing you to not have your period. Don't just have them do tests and not tell you anything. You need to be asking your doctor what the problem is, and what to do about it. I would probably call the doctor first and ask them what is causing this. If they need you to come in then they will tell you on the phone, and they can help you figure out what is causing this. If you do not have a doctor who will help you figure out what is wrong, then you need to go to a different doctor.