bringing up birth control to your overly protective mom

so a while ago my mom and I were discussing my skin and taking me to the dermatologist and she mentioned that she needed to talk to my doctor about putting me on birth control (because you know that can help) but I know that she's forgotten about that conversation because it was SO long ago, but I feel as if I bring it up its going to be suspicious because I have a boyfriend and she's just going to bombard me with questions like "why do you need to be on birth control, that's not something you need if you're not having sex, you're too young anyway, this that and the third" (I'm still a Virgin and I'm 18 btw) 
doing the dirty isn't the primary reason why I feel like I need to take both control, I do hope it will help with acne and irregular periods (not to say I WOULDNT eventually if I was on birth control, because I've made it completely clear to my boyfriend that it's not going down as long as I'm not on birth control and he understands) 
but yea, I don't really know how to bring up the subject. i love her but my mom honestly isn't someone I can talk to about sex (I'm a tad bit on the sheltered side, she continued taking me to a pediatrician instead of primary care doctor until after my eighteenth birthday, and when she found out my brother was no longer a virgin in like his junior year in college with his girlfriend of six years they got into a huge argument and I know since I'm the baby she would be mad at me just for bringing it up)
I know there's options like planned parenthood and if I do bring it up to the doctor on my own they're not supposed to say anything to her, but as I said a little on the sheltered side. I can't just come and go as I please do going to planned parenthood would raise questions, not to mention I don't really know much about medical insurance and I know I can't pay for it in my own.
in the mix of this overly explained situation, my question is more or less how do I bring up the subject of birth control without it seeming like I'm eager for her to help me get it so I can run off and have sex without the consequences of a baby