The first thing you need to do is think about what you want to say to your mom, when deciding to have the conversation with your mom you need to pick a time when she is not busy, then you have all the time to talk. You need to remember that your mom was young once too she probably had a similar conversation with her mom. Everyone's periods are different and we all chose to handle them in different ways. 

Hope this helps, remember your body is a beautiful thing. Good luck x