Can Having Sex Followed By Intake Of I Pill Cause Pregnancy?

hi..I am 23yrs and have a regular cycle ...I had *** on the 21st day of my cycle,, (where generally the cycle is of 21 days duration) and took an ipill within 48 hrs but after 24 hrs. I should be expecting the next menses by now (29th day),, but so far no luck..did the pill work?