Chance of getting pregnancy

Patient: Hai i am 25 years old. i am taking primolut N tablets for 5 days to delay my periods.. last month my period started on 19th july and this month i am taking primolut N tablets from 13th of this month to delay my periods.. i had sex on 18th august.. what is the chance of getting pregnancy??? Is it safe now to take i-pil or any contraceptive medicine? we are not planning for pregnancy now.. so please help me..

Symptoms: None