Hi, thank you for asking Microgynon is a combined oral contraceptive pill.Combined oral contraceptives like Microgynon work by over-riding the normal menstrual cycle The daily dose of hormones taken in the pill work mainly by tricking your body into thinking that ovulation has already happened. This prevents an egg from ripening and being released from the ovaries each month. The hormones also increase the thickness of the natural mucus at the neck of the womb, which makes it more difficult for sperm to cross from the vagina into the womb and reach an egg. They also change the quality of the womb lining (endometrium), making it less likely that a fertilised egg can implant there Once you stop taking the pill, the hormones are out of your body quickly, usually within a couple of days (this is why women who miss a couple days of pills on birth control have a chance of ovulating and getting pregnant!) Once the hormones are out of your system, your body will begin to start producing hormones to initiate menstrual cycles. Some women will begin to ovulate in a couple of weeks, whereas it may take several months for other women to begin to ovulate. Generally speaking, your body should be back to normal menstruation mode within two to three months after stopping the pill So dear you should not be worried, because your cycle has begin to work again, that s why you ve started bleeding. if you have any other question , please contact me again. Best regards, Dr. Ermira Biu