Maybe you should talk to your parents about birth control, and ask that you see your dr no matter what. Missing your period for so long could be because of something totally unrelated to pregnancy. Get yourself a calendar, or this website has a great app for charting your periods. You should be aware of when you're having them to make sure you keep up with it. And if you decide to become sexually active in the near future, it's a good idea to see a gynecologist. If you're scared to talk to your parents about it just tell them the truth, you've missed your period and are concerned. I'm not saying to lie to them...I'm sure it would be a big surprise if you were pregnant and the dr said that was why you'd missed them.
Take a test if your that late it would show up on a test if it's neg then call yourdr and get an appointment