How do I tell my mom I want to go to the doctor's to get a checkup?

I'm 14 and have a few questions I would like to ask him; I'm kind of shy, and my parents aren't too open about discussing sex.

Well, there are a couple of options here. It's difficult, but if you could somehow convey to your parents that you have a couple of questions regarding sexuality, they would probably understand. Even if they're uncomfortable discussing the topic with you, I'm sure they'd rather have you talking it over with a doctor than have you pick up misinformation "on the street." As an alternative, talk to your school nurse about it. Perhaps he or she can answer your questions, or refer you to someone who can.