plan b and period?

I had sex with my boyfriend on Monday October 24 with a condom but it broke and he ejaculated inside me. We didn't know it broke until we were finished. We immediately went to the cvs to pick up a plan b. I took it about 30 minutes later with a chili cheese dog and water. My period usually comes on the first of every month but it started on saturday October 29. Everything seemed normal. It seemed like a normal period. The next day I stopped bleeding like normal and started spotting. Blood would just drip one by one when I went to the bathroom and it stung when I peed. I think I got a uti but I think that's a totally separate thing. Is this a normal effect of the plan b on my period or could Implantation bleeding. On the first day, I had normal blood clots. The first day was totally normal. My period usually lasts 4 days but I'm barely spotting now. What could this be?