What Do Brown Spotting And Irregular Bleeding After Sex Indicate?

My period cycle is 6 weeks. I had unprotected sex 12 days prior to a small amount of brown spotting. The spotting gradually increased but not enough to soak a pad in a day. It also turned bright red for about a day then it gradually turned black and stopped. This happened over a course of six days with the heavier bleeding for only about a day. Could I be pregnant?