Do you lie to your doctor?

Why?

I don't want to but I feel like since I'm underage for drinking I shouldn't say admit it and weed is illegal so I don't say that either

Your doctor is meant to help you, not get you in trouble. She can't help as well as she could if you lie to her, and she is bound by law to keep everything you tell her to herself.

That's true. Plus since I'm over 18 now I can tell her not to tell my parents anything

I'm pretty sure you could do that when you were under 18 too.