Hello Duphaston is one of the most used drugs to regulate the menstrual periods. It contains an active substance called dydrogesterone which acts like the progesterone (female sex hormone ). Progesterone works by preparing your uterus lining to recieve your fertilized egg and if it s not fertilized ,the progestrone level will drop and your menstrual cycle will begin . Your doctor has prescribed that medication to regulate your cycle, by preparing your uterus like the progesterone does, when you take the last dose ,that will be similar to the droping of progestrone level and you will have your menstruation the next day . For your concerne about miscarrige , duphaston will not cause miscarrige, on the contrary it s used to treat threatened miscarrige and it helps to fix the fertilized egg in the uterus. You should absolutely loss weight to have a regular cycle cause the obesity affects the hormonal regulation of the menstrual periodes . Hope I answered your question Best regards Dr.Noor Farid