What Causes Irregular Periods In Spite Of Taking Duphaston?

i missed my menstruation for two months.. i went to a doctor and she prescribed me provera.. a week after taking it, i had my period... she asked me again to take duphaston on my 5th day of menstration, for one week... now, 8 days after taking the duphaston, i had my menstration again.. but it's only little... what is happening to me? is it normal? should i take duphaston again?