Thanks for the query.
Emergency pill can alter the menstrual pattern.
It can prepone the bleeding, if you took the pill in the first half of the cycle.
So as you took the pill in the first half of the cycle, that might have led to withdrawal bleeding.
Emergency pill can also lead to side effects like intermenstrual spotting, pain abdomen etc.
This occurs due to hormonal
For more details : http://srsree.blogspot.com/2012/08/emergency-contraceptive-pill-short-term.html
Usually these will subside soon.
If pills are taken repeatedly that can prolong the side effects.
There should be at least 2 months gap between two pills.
You wait and watch for few days, if the pain and spotting persists, better to consult gynecologist once and get examined.