It depends on a few factors. Normally, emergency pills like Sendinor, Postinor 2 and post pills work when you use it within 72 hours of having unprotected sex. The longer it takes you to use it after emergency sex, the lesser it's efficiency. All the best

Go and do a pregnancy test quickly

Its possible dear, some ppl even ovulate while menstruating.

IF the drug was taken within 72 hours after the sex, there should be no cause for alarm.