While I don't condone lying, if you are having trouble figuring out how to go to the doctor, since there are payments due, etc., without your parents' knowledge, I suggest that you start by telling your family that you're sick, don't feel well, whatever you need to say that's believable. Get them to take you to the doctor. If you think your mother would come into the examining room with you, have a note prepared ahead of time that says, "i need to speak to the doctor alone - without my mother, please help." the nurse will make sure that you have that opportunity. Then, tell the doctor what's going on. The truth. All of it.
I don't know how old you are, but I was pregnant when I was a teenager and am now the mother of 6. My father and mother were not parents that I felt I could go to for help, but things have a way of working out. If you are pregnant there is a lot to think about. But there are options. Feel free to send me a message or e-mail if you need to talk. I think you can just click on my name and get to my profile for information on how to do that. If not, post a reply here. I'll see it.