I'm on Levonorgestrel and Ethinyl Estradiol monophasic combined pills.

I had sex about an hour and a half ago. I just went to the bathroom and found that I have started bleeding. I didn't really feel any pain.
I have been taking BC since Sept 2013. The latest I've taken a pill on this pack is 12 minutes. I haven't missed a pill before. We had sex with a condom.

What could this be? Could it be that I simply got hurt or could it be something more serious? I am very very worried.
Thank you