Bleeding red blood week after period?

Hi everyone, I’m currently baffled at what is happening with me right now. I got my normal period on 12/7 and it lasted around 4 days (normal) then after that I proceeded to have my usually spotting of black blood but today, I woke up with bright red blood dripping down my leg (as if it was the start of my period again) should I be concerned? Also, I had taken a plan b on 12/10, around the 3rd day of my period. I’m also having period like symptoms. Is this some sort of side effect of the plan b?