Bleeding 3 days after my period ended

Dre

Hi! So I ended my period around 3 days ago and this morning I noticed I am bleeding again. I have been sexually active and I took plan b on Wednesday (today is Saturday) because I am not on birth control. Does anyone know what may have caused this? I was it plan b? I don’t think it is implantation bleeding because that usually happens 8-10 days after conception. Please help!