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is a emergency contraceptive pill
and is to be taken with in 12-24 hours after unprotected sex.Since it is a hormonal
pill normally you should get bleeding (like periods) with in 1 week of taking the pills.Since you have used Postinor2 for 4 times in this month that is 8 tablets I feel due to the pills the periods have delayed as there should be a hormonal problem caused by the excess of pills.As you are apprehensive you can get a pregnancy
test done but I am sure you should not be pregnant and the missed periods are due to pills.Wait for 7-10 days if you are not pregnant and if you do not get periods please consult a Gynaec for treatment.Hence forth if you are sexually active and have sex more than once a month please get a regular 21 day birth control pill prescribed by the Gynaec so that it will help you to avoid pregnancy as well as keep your periods regular.