I had unprotected sex when i was suppose to get my period i'm irregular in my cycles i took plan b can i still get pregnant ?

Plan B would: markedly lessen changes of pregnancy. Plan B One-Step is up to 89 % effective when taken within 72 hours (3 days) after unprotected sex. It can reduce chance of pregnancy by up to 95% if used within 24 hours. It continues to reduce the risk of pregnancy up to 120 hours (5 days) after unprotected sex, but is less effective as time passes.