Something weird is going on I need your opinion..

Ok so my period ended around Sunday or Monday and I believe Wednesday i discovered I had a lot of old blood in my underwear. I honestly thought I shitted myself until I smelled it 😂. Now it’s Friday...and I’m still having tones of old blood. My boyfriend and I had sex near the end of my period and he came inside of me (here come the judgemental comments🙄) but I took a plan B later that day. Should I go to the doctor or just blame it on the plan B? Btw I would show you guys a picture but it’s pretty gross.