Spotting instead of period. Pregnant?

While having sex a couple nights ago, my partner pulled out and found some blood on his penis. He is very large, and I believe he may have bumped my cervix, which I understand can cause light bleeding. But I did not experience any vaginal or pelvic pain during or after the sex. I also thought it might be my period, since this is around the time it should come, but it hasn't gotten any heavier than a light pink/brown spotting (this is the third day of the spotting). I went off the pill almost a year ago, and my periods have been normal for the past four months or so, other than now. We have had a lot of unprotected sex for about a month, so I didn' t know if this bleeding could be implantation bleeding, or simply a light period?