Bloodwork and drug testing.. Terrified?

Im 17 and in the us. My mom just informed me that i have to have bloodwork done today.. They are taking my blood and probably making me pee in a cup. Its for the doctors.. My mom wants my iron levels tested because she thinks i might be deficient and is probably having my cholesteral checked. Ive had to fast for the past 8 hours and there is a significant amount of marijuana in my blood. I started smoking a week ago and have been everyday since then, including yesterday. Will they find any type of drugs in my system? How do i know what they are testing my for? Im a minor so they can tell my mom everything cant they? Please help