is a very effective contraceptive
method with failure rate of about 0.5%.
What is your age? Were your periods regular before seven years? While on pills it is natural to have regular cycles.
Usually menstrual cycle revert to your previous pattern after stopping the pills. Occasionally they can be become irregular specially after 40 years of age due to hormonal
variations and this is normal. There is also a very slim possibility of pregnancy
as a result of tubal ligation method failure.
So I advise you to take blood pregnancy test as it is more sensitive. If it is negative consult your doctor and take progesterone
tablet for withdrawal bleeding. if your next cycle is also irregular consult gynecologist to determine the cause.
I hope I have answered to your satisfaction.