bleeding? should I be worried??

So me and my bf had unprotected sex and i’m not on birth control (pls save the lecture comments i know it wasn’t the safest choice) and i believe that he did finish a little bit inside of me. so the very next day i took a plan b. about 4/5 days later i am bleeding like as if i’m on my period. i don’t know if i should be worried or not. thank you

side note, i’ve had no other “symptoms” other than this bleeding other than a sinus infection that’s been going around

another side note, i was not ovulating when we had sex, it was actually on the very last day of my period