Early bleeding?

I've been on the pill for almost a year and my periods are usually very regular as a result (they always come during my placebo week and never really before). This cycle, I started bleeding a week early and haven't stopped (one week before my placebo week). My placebo week is next week. I don't think it's due to pregnancy, and the only other symptom that I have is cramps. Otherwise I'm pretty much healthy. Could it be due to stress (I was really stressed around when I started to bleed early)?