welcome to HCM.
You are suffering from irregular period.If you stop to take duphaston
,a withdrawal bleeding is present and not to confused with normal period.
There are several reason of missed or delayed period like hormonal
imbalance,stress,irregular eating habit,ovarian cyst
,thyroid problem etc but have to exclude pregnancy
You do a fresh USG lower abdomen and hormone profile to rule out underlying pathology.
Then consult with gynecologist and take advice accordingly.