[Sinner]

I'm sixteen, and I went to the doctor the other day to get checked for a UTI. She asked all the usual questions, and I told her I was sexually active, how many partners I've had, etc. etc.
Afterwards, she started talking about how I need to be on birth control and stuff, and ran a pregnancy test. It came back negative, but she rescheduled me for an appointment next week for a female exam and another pregnancy test.
My parents are extremely religious, and think I'm the epitome of wholesomeness. They don't know I'm having sex. They don't even know I've had a boyfriend. My mother is getting really suspicious about all of this, and is demanding to go back with me when I get the exam and tests taken care of. I told her it was a checkup on the UTI, and the exam is something they do regularly for teenage girls. Well, she keeps saying she doesn't know why it would be necessary to have it done, since I'm only a teenager, etc. etc.
If she goes back there with me after the tests and exams, what is the doctor allowed to tell her? If I do have something, or am pregnant, will the doctor tell my mom, or tell me first? And how can I get on birth control without my mother finding out all of this?