Hi! My Last Period Was Last Feb 26 This Year

hi! my last period was last feb 26 this year and i only had around 4 days, and last march i didnt have any at all already, giving myself for another week before i went to a doctor. The OBGYN says " congratulations, you are not pregnant". She prescribed this so called Duphaston for me to take 2x/day and i waited and waited for the day that my period will come but it didnt. So i went to a pharmacy to buy pregnancy test kit and as well shown it to them this medicine, so they ask me if im pregnant but i said im not. i quickly try the test in my place and its negative. but ive got this history of previous miscarriages. what could be the doctors purpose of prescribing this medicine to me? thank you and will wait for your response