I'm twelve and I have questions about my period?

I'd ask my mom , but you know , shes asleep. Anway , I have had my period for about a year now . For the first 3 or four months, i would have it in the middle of the month. Bewteen the 5 and 9 months, it started getting earlier. And Now it started happening between the 1st and 3rd of each month. This month, I started my period today. Is that too early ? I havent had sex and i dont think Mstrbtion can cause it. So any help?