What Causes Period Symptoms In Spite Of Taking Contraceptive Pill?

Hi my fiance and i had unprotected sex, the day before my egg should be released (1 to 2 days after my period). The next morning, right before twelve hours I took the ´morning after pill.´ Again, twelve hours later, I took the second pill.. Now two days later i am getting a cramp or back pain unusual to period cramps. Is that it working, more likely? Or more chance of a little baby growing? :)...