Confused and need help?

ok i have irregular periods which is supposed to come around the 23rd or 24th. i dont know if i was ovulating on the 17th. im confused because it says the egg can only last for about 24hrs w/o a sperm fertilizing the egg. if this is so how will i know if my egg was fertilized. i know that if there is no fertilization then my period will com on but this whole process is confusing me so i need all the help i can get thanx a million