Postinor-1 can prevent you from becoming pregnant if you take it within 72 hours of unprotected sex. It does not work if you are already pregnant. BTW you have taken it within 5 hours then there is 0% chances of getting pregnant.
The reason is why you are not getting your period is, That medicine which you took for 3 days. No need to go to the doctor just wait for sometime and you will get your periods.