Hi I Want To Know About My Pregnancy.last Month 17th

Hi I want to know about my pregnancy.last month 17th my periods was happen.1st 2days its not a complete blood and next day it complete.last month i used postinor 2 tablet in twice a month.using date of postinor2 is very close to periods date.but its not effect for that.in this month 14th i was having protected sex with using condoms.my problem is that.what is the reason for delay my period.my periods dose not happen yet.plz answer me