from plan b?

so i had unprotected sex may 12th, which was one of the last days on my period (which is usually only like 4 days long), i took a plan b 2 hours later but it made my my period like four days longer and now this month i haven’t got my period, and i’m scared i could be pregnant but i haven’t gotten any other symptoms, is it from the plan b or should i be concerned??