I'm 17 years old and haven't started my period yet, is medroxyprogesterone safe?

I have had many different tests done by my doctors to be sure that everything is okay, which it is! They finally came to the conclusion that I'm just a late bloomer, she prescribed me a med. that would help me start, Medroxyprogestrone. I got it and was going to take then I started reading more about it, the risks and side affects have began to worry me a little bit. My mother, an RN, has told me I'm just being a worry wart about the whole thing not to think about it so much, that they just put those risks on there for people with medical problems that may lead to some of the things on the list. But it says things like, Heart attack, stroke, breast cancer, blood clots in the lungs, and legs, and possibly other cancers. I'm just second guessing whether to take it or not, I only got it because I wanted to start my period now, I've gotten tired of waiting and becoming more and more worried that it's never going to arrive. Is there other things I can do to help start? Should I take the medicine? Or should I just wait it out and see if I start on my own? And could anyone tell me the lastest age that is normal to start your period?