Birth control

Hello, i’m 17 years old about to be 18.

I need to go to the doctor because i have a cold, my questions are:

Can i ask her about birth control ?

Will she prescribe it to me or do i have to see a gynecologist?

I’m not sexually active and i probably won’t have sex until i’m 21/22.

Also:

Will i gain/lose weight if i take any kind of birth control?

Thank you very much