Implantation Bleeding

Has anyone experienced this? I was on the patch 7 days before I had unprotected sex. He pulled out. I also took plan B in 10 hours. Under normal circumstances that would have been the day I ovulated. I noticed 11 days later I'm getting a very light pink discharge and mild cramps. Could this be a symptom of Plan B or does this sound like implantation bleeding. I really don't want to have to make a decision whether to abort.