Can you legally get a perscription if you're 18 from a doctor?

I'm about to turn 18 and for the past couple of year it's been significantly harder for me to concentrate in school, im constantly tired and restless and can never to fall asleep when i'm supposed to. I believe i have a mild case of ADD or some form of sleep disorder, however I haven't discussed this with my doctor since my parents health insurance still only covers for me to go to a Pediatrician and I'm worried what my parents will think if i have some sort of disorder. My parents don't believe in perscription medication, only if it's for something severe and I don't even really take Advil or anything. However, my friend has ADD and i seem to share alot of her symptoms, and I've tried her medication once (don't lecture me, I know it's wrong) and it worked wonderfully. I'm turning 18 very soon and since I would be considered a legal adult I was wondering how I could obtain a perscription for Adderall and around how much it costs.