Spotting.

My period was supposed to start today (Monday may 5th). Two days ago I thought I started my period because I was bleeding a little, and I put in a tampon and the 4 hours later there was not even a single drop of blood. I would say the bleeding had lasted for 10 minutes top. The color was light red. I do have unprotected sex and the guy I'm with has had a couple times where he didn't pull out. So I know I have a chance I could be pregnant, but I just want to know if this is what spotting is or does it usually last more then ten minutes?