Why Do I Experience Brownish Discharge During Menstruation Instead Of Normal Bleeding When I Am Diagnosed With PCOS?

I have been getting brownish discharge mostly during my periods since 3 months before I used to have heavy blood flow now it s very little and since I have pcos my periods are not regular..my doctor prescribed me douluton L years backs and i have been using it on and off..i am unmarried and prolonged periods with light flow ..what to do?