Hi. Thanks for asking in Healthcare Magic. Norethisterone is a progesterone. It delays the period as long as it is taken and results in withdrawal bleeding within 3 to 4 days of stopping it. This is due to the sudden fall in the hormone level. Hormonal pills when taken, will alter the existing hormonal balance in the body and hence may result in change of normal pattern. Such a practice should not be attempted regularly especially if you want to conceive. Your next period may be delayed or it may start on 6th. It varies in each person. Further periods may be regular. Ovulation kits are available to find out the time of ovulation. Rise in early morning temperature, more thick and viscid cervical mucus secretion and pain in the lower abdomen will all indicate ovulation. I hope this is useful to you.