Thanks for the query.
can cause side effects like pain abdomen, spotting etc.
As you took the i pill within 72 hours there is possibility for protection.
For more details:http://srsree.blogspot.in/2012/08/emergency-contraceptive-pill-short-term.html
But sometimes it is said that when pill is taken after 24 hours the degree of protection will decrease.
So now you just go for symptomatic treatment like antispasmodics.
If you miss your expected date of period once go for blood test
which will rule out the possibility.
Depending on the result further management can be taken.