Have you been having sex? If you have, get a pregnancy test. Or, have you lost a huge amount of weight/started exercising a ton? If not, you should probably go see a doctor, because that doesn't usually happen. I had breaks of 5 months the first couple years of my period, but not after it became regular. Actually, you should probably just go see a doctor sometime soon (preferably someone in ob/gyn). If your parents won't take you, you can go to somewhere like Planned Parenthood (which has a sliding scale fee).
Nope, I have not had sex. And I've been playing basketball since the middle of November. But this hasn't happened before during a basketball season.