Sex, plan b, then bleeding

so i had protected sex then we had sex again but unprotected two days later i start bleeding i don’t know if it’s because i was dry when we had sex or because i’m pregnant but you can’t start spotting that early am i right ? so i took plan b between the 72 hour range and now i don’t stop bleeding it’s very light i don’t know if i’m pregnant or not. is it too early to have a pregnancy test ? by the way the second round of sex we had he did not cum