I haven't had my period since late August?

Well I'm only 13, so I know it's not because I'm pregnant. I just find it weird that I haven't gotten it in such a long time.. I've gone 2 months without my period several times. And I've had periods that lasted for only one day, and were super duper light before. I could just use a liner and I'd be fine. But I've never gone this long without it! I've had it for almost 2 years, so shouldn't it have a pattern by now? Mine always completely strucks me by suprise. Does your eating habits effect your period? Because mine have been pretty hectic, since school started.