Suggest Remedy For Periods Problem After Taking Duphaston

i am 30 yrs old. i never had any prob of periods. i always had sufficient bleeding during cycles. after completing 3 yrs of married life me and my husband planning to have a baby. for this reason i went to the gynac on february..and she gave me letoval and duphaston for 2 cycles. during taking those medicines i am finding that my flow is less during cycles for the last 2 months. what could be the reason?