What Causes Bleeding During Intercourse?

The first day of my last period was Feb. 13. I started the pill (ortho tri cyclen lo) on March 1. Today during sex I started bleeding. Assuming I didn t start taking the pill, my next period wasn t supposed to start until March 13. Could the bleeding be my period, or caused by the fact I started the pill mid-month? Is it recommended that I stop taking it and start a new pack after the end of my last period? The blood was red, like fresh blood, but thereafter, it was dark/brownish I don t want my period to become irregular.