May 15th & 16th , I had unprotected sex while on my period. Even though my period continued I got a plan B on the 18th. 5 days later I started bleeding, which I thought was the plan b working, the blood started off brown & ended the next day Bright red. Now A week later I'm cramping like crazy & just feel weird & my next period isn't due for another week. Could it had been implantation bleeding?