Emergency contrceptive drugs are basically high dose hormones given in one go. They can cause premature bleeding prior to the expected cycle, in form of spots, clots, bleeds and even normal periods. If taken closer to the next due date, they can also delay the expected period by a week or so. What you need to do is to stop emergency pills till you get the next regular cycle. And if you are likely to remain active sexually, then take a regular pill instead. It is safer and does not cuse cycle irregularities.