Help please...

I'm 15, and I kind of want to get on the pill. Not just for sexual reasons, but I want my periods to be normal.. they're usually 2 weeks long and I've told my dr. and she said it's normal for someone my age, but that's not true. So can anyone give me some advice? I'm kinda nervous to talk to my mom about it, because she will think that I just want it for sex...