Why Is Duphaston Prescribed For Irregular Periods?

Hi , i have irregular period , my doctor i have been prescribed with Duphaston to have my periods after that , i have taken clomid for 5 days ,and then continued with glucophage and diamil .. on my 11th day doctor also did pelvic sonar which shows normal grown up folicles ... now my doctor still asks me to take dufaston on my 16th day as i mentioned earlier , wil this not let me have periods ...will i be pregnant as my follicles are showing the right growth