Hello, I am afraid that it is not clear from your question whether a doctor suggested you to start with norethisterone or you are following advise of a friend from her experience! I would like to caution you that every case is different as far as menstruation problems are concerned. For your irregular menstrual cycles, any factor might be responsible like cysts in ovaries, thyroid gland malfunction, infection in the uterus or ovaries, or some structural abnormality of uterus or ovaries. I would advise you to visit a gynecologist and go for blood tests for hormonal levels as well as ultrasonography. Based on the test results, diagnosis can be confirmed followed by appropriate treatment. If you will take norethisterone for 7 days, it will cause menstruation after 2-3 days of stopping the drug. However, next month, you may or may not get periods as it is not a medicine for your disorder. Norethisterone is used to delay periods or treat premenstrual syndrome symptoms. I hope this information helps you. Thank you for trusting HealthcareMagic. Let me know if you have any follow up questions. Best, Dr. Viraj Shah