Help..

So I have a doctors apt at 3:30 today to get put on birth control and they said my mom has to go with since I'm not 18. However I don't know what to tell the doctor. I've had sex before.(haven't since like August) but I don't want to tell them I am and have my mom find out but if I ask for her to leave she might realize. Will it hurt if I don't tell them yes and say no I'm not? Help?! I'm freaking out!