I m having a missed period after using emergency contraceptive pills thrice..nd i had breakthrough bleeding i guess.is this normal..

Yes: Emergency contraception is meant as just that--not a convenient substitute for planned birth control and std prevention. It profoundly disrupts your cycle, so expect irregularity.

Not unusual: not unusual for this as it causes a change in the hormones that your body will need to adjust to. If worse or persistent, would recommend check up. Would have a pregnancy test performed as well.