NEED ADVICE! HELP!!!

Chayla
I had unprotected sex Dec 4; the condom broke and everything. The next morning(Dec5) I went and got Plan B and took it within 12 hrs of having unprotected sex, on dec 12 I started what looked like my period and it was pretty heavy it is now Dec 15 and it's ended, I'm also having some lower abdominal pains almost like cramps. Is this just side effects from taking the pill or should I be worried?