How do I make my mom leave me alone?

She is clingy, overprotective, mean, depressing, obsessed with power, ect. well next month on the 30th(my birthday,) I'm taking my girlfriend up to cedar point(amusement park in Sandusky Ohio,) for a day or two. Well my mom is a super b*tch and is saying that we aren't allowed to get close to each other, not allowed to go off on our own and not allowed to be alone with each other. She's 16 and I'm gonna be 16 on the 30th and we've already had sex. My mom knows about this and I think that's why she's doing this. How do I get my mom to leave me alone? She doesn't listen when I ask about it and starts an argument about it. She's acted this way before and it almost caused my gf and I to break up cuz she wanted a more intimate relationship, which my mom won't let happen. If she sees me so much as hold her hand she flips out and grounds me. idk what the hell is wrong with her but it's destroying one of the only things I have left. I love my gf very much and want to enjoy this trip but I can't do it with my retard of a mom. Help?