When a woman goes off a hormonal contraceptive, such as the Depo Provera or birth control pills, it can take up to six months for the ovaries to “wake up”. When this occurs the ovaries begin ovulation again and start producing eggs so that a woman can conceive. She will begin to have regular cycles.
Sometimes the body needs more time for the ovaries to start working. It is always helpful to keep a menstrual calendar to find out if there is a pattern to the irregularity. Over-the-counter ovulation kits are useful to determine the fertile windows in order to help with conception.
You should also speak to your gynecologist in order to find out if there are any other causes for the irregular cycles that will also prevent conception. Other conditions, such as a low thyroid level, can prevent ovulation, leading to irregular cycles and the inability to conceive.