Why did my period randomly come?

Okay so I got my first period when I was 13. I'm 15 now. I always have had a normal schedule. Im not sexually active either. So I was sitting in Spanish class and I get my period. I'm 2 weeks early. Im not on brith control pills either or have been stressed too badly. I only bled a tiny bit. It happened early today. Whats going on?Why did my period randomly come?
If it's two weeks early, I would think you are smack-dab in the middle of ovulation - some women experience a very small amount of bleeding while ovulating.
If you have experienced a change of diet, that might do it. Or if you have recently stopped using ibuprofen to treat period cramps - my friend used to take a lot of ibuprofen for cramps, and then when she quit, she got her next period just 21 days later.
If it happens again next time, you might want to go to a doctor just to be sure. But uteruses just do strange things every now and then, so if it's an isolated occurence, I wouldn't worry. Good luck!
Your body will ultimately bleed however it wants for its own schedule when it wants! You are only 15 your period is gonna take awhile to get regular so to speak. Im 22 have two kids and my period is retarded too!
Many things could going on...your body is still (although it has been 2 years) getting use to everything...you could be under stress although you may think differently...you could be ovulating, that can cause spotting (what you described) It sucks...I know