What Causes Abnormal Bleeding After Periods?

About a week ago I had started my period, it was a normal cycle for about a week. Then I was done bleeding for a couple days after. During them couple of days me and my boyfriend had unprotected sex and had an accident, the day after the incident I started bleeding again. Its not a normal period though, its very very light, and i've had it for about 3 days now. Whats going on?..could I be pregnant?