What Causes Spotting And Bleeding With Abdominal Pain And Backaches?

I'm on lo seasonique birth control, and have been for 4 and a half months. My boyfriend and I fooled around a little, the next day I experienced bad abdominal pain along with backaches, this has been going on for 3 weeks. About a week and a half ago i began spotting and bleeding, but it changes colors and i get what feel like period cramps.. Do you have any answers as to what this could be?