What Causes Irregular Periods With Light Spotting?

My period is very late, 8 months to be exact. But, I think my period did start, but ever since it started, my result was extremely light flow, with only brown and sometimes red blood. 90% brown, 10% red, I would say. It's so light, it could be spotting. I'm 15, a virgin, and did not take any drugs or pills ever. My periods started at when I was 13, and is regular until 8 months ago. Please help me!