What Can Be The Reason For Delay In Periods?

on june 9 i had unprotected sex with someone who has had a vasectomy. 48 hours afterwards, though, i went ahead and took plan b to be safe. two weeks (june 25) later i bled for about 5 days, though it was light. considering i have regular 29 day periods, i should not have been ovulating until 3 days after the sex, at the earliest when should i expect my period in july? do i go off of when i bled in june, which means i should have started my period yesterday (july 23) or do i go off of my last normal cycle, meaning i should start my period within the next couple days (given my regular 29 day cycle)