Thanks for the query.
As you took the plan b
within 72 hours the protection from pregnancy
The pill can disturb the menstrual cycle pattern and can alter the time of period.
For more details:http://srsree.blogspot.in/2012/08/emergency-contraceptive-pill-short-term.html
So the symptoms you are experiencing could be more possibly side effects of the pill.
You wait for one more week, possibly by that time you will get your periods.
Meanwhile you can take symptomatic treatment.