What Causes Light Spotting During Periods?

Hi, I'm really concerned about this. Now, I don't know if it's just because of the month being February, but I had sex on the 10th. My partner didn't come in me. I wasn't ovulating then. I thought my period was supposed to have come a couple days afterwards. On the 13th, I noticed that there was very pinkish blood present. Now, it's slowly turning red, but still flowing lightly. Could I be pregnant, or is my period just changing ?