How Would I Know If The Emergency Contraception That Has Been Taken Is Effective?

Hi My periods started on 22nd of July and ended on 26 of July. My cycle goes for 21 days and a times extends to 23 days. I had intercourse on 31st of August but took the emergency contrecpetives before the end of 24 hours. I later had sex on 5th of August but never took the contrecpetives. I do not know between the two dates when I conceived and it is a matter of concern I would like to know if the emergency pills failed or I conceived on a later date Please help