Convincing my mom for an IUD?

I've been having a lot of unprotected sex- and when I say a lot, I mean since October of last year. We use condoms when we have the chance, but my parents don't approve of me being sexual active, so most of our sexual encounters are spontaneous and random, and we often both are unprepared. My mother snooped through my phone and found out that I had sex once, back in January. She told me no more sex. But of course, that isn't happening. I just want to be safe and make sure that I don't get pregnant. I went to the doctor and asked if she could convince my mother to allow me an IUD for period irregularity, but she hasn't set up and appointment and keeps putting it off. Is it better for me to get it at Planned Parenthood? The sooner the better. I'm unsure of what to do :(