What Causes Spotting?

hi i started my period on the first of this month and it lasted five days. i had unprotected sex on the 11th but he pulled out. i took the day after pill on the 13th. today when i woke up i wiped and had a little discharge so I wiped again and had a little more. This has never happened to me but when I went to the bathroom a few minutes ago I didnt have anything. Do you think this could be pregnancy?