Hello, Thanks for sharing your health concern with us. Emergency contraceptive pill contains high dose of progesterone and hence can cause menstrual disturbances due to altered hormone balance. It should be used only once or twice a year and not more frequently. You need not worry about pregnancy during this cycle since you had the intercourse during the safe period. Ovulation occurs two weeks prior to the onset of the next menstrual cycle and this is the fertile period when an unprotected intercourse can cause conception. Your period may have been delayed due to the use of Regestrone. Please wait for a couple of days and get further help if you become overdue by a week. Take care.