What Causes Light Spotting Between Periods?

I had unprotected sex on October 19th. On November 9th I started spotting a light brown, this lasted for a day. On November 11th, I started bleeding a bit, but then I had the brown discharge. The next day I woke up and there was nothing, even when I wiped. It is now November 14th, and there is still no sign of my period. Could I be pregnant?