Bleeding starting a few days early, not on sugar pills yet

I’ve been on pill birth control for 10 months and never had an issue. It works great and it’s helped tremendously with the timing of my period and the severity of my cramps. Up until today my period would start after my second or third sugar pill. Every month since I started birth control. I have a huge irrational fear of getting pregnant so I take it every night at the same time. Never missed a pill. I went to the bathroom tonight and had a light amount of dark blood on the toilet paper and a spot of dark blood on my underwear. And I still have one regular pill left before my week of sugar pills. Any reasons to why it would start early?