Hi Thanks for posting on HCM Missing period while on combined oral contraceptive is normal especially when you just start. Changes in the uterine bleeding pattern during or between menstrual periods (such as decreased bleeding, breakthrough bleeding or spotting between periods, prolonged bleeding, complete stopping of menstrual bleeding that occurs over several months in a row, or stopping of menstrual bleeding that only occurs sometimes) are normal with Dian pill. A negative pregancy test if with valid pregnancy test kits, eliminates pregnancy.You may not need primlut N to trigger menses.Just known absence of period is normal. Hope this will help Best regards