What Causes Light And Prolonged Bleeding While On Trinessa?

I've been taking Trinessa for about 3-4 months now. I haven't missed a pill, although I haven't been taking the pills at the same time every day. Sometimes I take 2 pills a day due to forgetting. I have been having unprotected sex with my husband since being on Trinessa. This month I got my period a week early from when I'm supposed to start, and I bled for 2 weeks straight. Not very heavy bleeding, but still bleeding. I am wondering what the chances are of me being pregnant?