actually, you should consider yourself lucky that you've managed to go six months without seeing the doctor again! most doctors will require a one month check up, then a three month check, and then a six month check.... after that, as long as you don't have any issues, then they usually let you go another six months to a year before another check up.
as the previous poster mentioned, adderall can cause high blood pressure, plus various heart problems, plus some people use it as a recreational drug.... so no, it's not unreasonable at all that your doctor would require another check up. i'm just surprised it hasn't been done sooner!