** Thanks for contacting with your health concern. 1. . As you are dealing with irregular/delayed periods for which you were prescribed Duphaston [dydrogesterone] tablets for withdrawal bleeding, which provided symptomatic relief only so consult a Gynecologist or for a second opinion, since it can be upsetting and confusing when your period is late and there are no positive signs of pregnancy, so it could be due to certain lifestyle changes like: - excessive stress - loosing or putting too much of weight - heavy exercises - suffering from PCOD [polycystic ovarian disease] or having a high level of prolactin [hormone] 2. other common causes which can delay regular period: - stress which disrupts the ovulation: causes your body to secrete more cortisol which delays or stops ovulation altogether causing irregular periods - Also, a diet low in fiber and high in saturated fats can cause irregular periods, likewise low thyroid [hypothyroidism] can also cause the same, so check with your Doctor. 3. Another commonest cause is functional ovarian cysts which will prevent bleeding so get an abdominal USG done to exclude the same. PS. It is best to seek suggestion to know why you have missed your periods, a Gynecologist would be ideal to consult, for appropriate examination/investigations. PS. Duphaston [dydrogesterone] is used for menstrual disorders and as hormone replacement therapy, and if periods don t occur after taking the drug, the most common cause is pregnancy, however as you said: you are not pregnant consider getting treated for PCOS and rule out other causes that could be responsible for delay periods.