Thanks for the query.
If you have taken the emergency pill within 72 hours of the unprotected intercourse
, possibly it will give protection against pregnancy
Emergency pill can alter the menstrual cycle depending on the period when you took the pill.
For more details:http://srsree.blogspot.in/2012/08/emergency-contraceptive-pill-short-term.html
As you interfered the normal cycle by taking the pill, it will take sometime for regularization of the cycle.
and strain can also lead to menstrual irregularity.
So you once consult gynecologist and undergo physical examination, then with her advice you can take tablets for withdrawal bleeding.