What Causes Heavier And Darker Periods After Taking Pill?

Hi, I'm 25yrs of age and about 64kg with a height of 1.5m tall. I had unprotected sex with my boyfriend on the 14day day of my cycle. After three days I took in some drug. I had my menses at the reguler time but just that the flow was heavy and dark brown in the first two days. The flow then turned into red on the 3rd and 4th day. Please tell me what is wrong. Could I be pregnant?