What Are The Side Effects Of Emergency Contraceptive Pills?

i have an uid fitted in in january and also i take a contraception pill gor my acne too. recently i have not been taking those pills n i have had sex wi my partner. the thing is i had sex before my period (after the 28th tablet) and after a week of that period ended i am bleeding again but its soo much heavier and i get really really heavy cramps. i have not experienced this before. what is wrong with me?