Hi, Thanks for the query. There are various causes for irregular periods. The commonest cause are hormonal imbalances in thyroid, prolactin, FSH, LH, DHEAS, testosterone etc. Other cause is menopause [I do not know your age] and pregnancy in sexually active women. Ovarian tumors also cause irregular periods. Primoluet N is a hormone similar to progesterone. Progesterone comes to act in the later part of the cycle after ovulation. It needs estrogen to exert its action. In normal cycle, when levels of progesterone decrease the uterus is not able to help the uterine lining to grow and results in its shedding in the form of periods. Not getting a period after taking primolute indicates that either there is already very high progesterone in the body as in pregnancy or very low estrogen not allowing the progesterone to act. Knowing your age and reproductive history would have helped a lot in narrowing the diagnosis. However I suggest that you get a gynec examination and ulltrasound done to look if the uterus and ovaries are normal. If they are normal a hormonal evaluation would be needed to know the cause. Hope I was able to help you. feel free to ask any more queries that you may have. Thanks for using HCM. Dr Madhuri Bagde Consultant Ob Gy