I Need Birth Control and I'm 18?

I recently turned 18 and I want to go on birth control. This is partially because I am tired of my random periods and partly because I would like to become sexually active. (I am not now). My entire family opposes birth control until marriage for religious reasons, but I would still like to get it without them knowing. I know I can go to Planned Parenthood for birth control, but I was wondering if there was an estimation of the price? Is Planned Parenthood automatically confidential? Also, when I go to a doctor's appointment/check up with my mom, how can I make sure she doesn't know? I know the doctors ask about medications and I can't tell them when my mom is in the room. Will they automatically ask my mom to leave the room, or do I need to call them beforehand and talk to them about it? Since I am legally an adult now, will they have to stay outside of the room for the entire time, or are there different rules involving a doctor's check up? I am just trying to stay safe and healthy, but it is so hard with my family, and I am terrified to ask any of my family members. Help please?