Welcome on HCM .
I hope I may be of some help to you.
Your girl friend took postenor2 after 5 hours of unproteted sex, is this right.
If so than she must not be pregnant.
But every contraception
method has some failure rate hence there is tension and this stress
itself cases for periods to go.
So fist get relaxed and think that tension will not solve the problem on the other hand will aggravate it.
As per your expectancy of period you must get pregnancy
test of urine done on 15th of April if periods are not there.
And report here with your expectation and certainly we will guide you.