Good day i took an emergency contraceptive after having unprotected sex on the last day of my period. 3 or 4 days later i began bleeding again. it seems like a very heavy period. what could be causing this problem? should i be worried?

It can happen: Plan B (or other "morning after" pills) can alter the menstrual bleeding for the cycle in which Plan B was taken, and sometimes in the next cycle too. One should be sure to check a home pregnancy test about 3 weeks after sex, because emergency contraceptive pills work most of the time, but not all the time. If bleeding is too heavy, one's Ob-Gyn doctor can examine to see if treatment is needed.