What Can Cause Vaginal Bleeding While Taking Duphaston?

i m havin pcos since 6 yrs,im now 30,married since one and half yrs..was takin treatment since marriagi,had one miscarriage on 45th day one yr back.all my hormone profiles re normal.i uderwent induction with letrazole 2.5mg,follicular study.my lmp was 3rd jan.i started taking duphaston from day 17.my ogcian asked me to contiue 10 mg od for 15 days.the problem is that i got bleeding on 16 th day of my prescription,that is one day before my drug to get over..why this happens,,is it my periods?or somethig unusual or i m pregnant?.can we get bleeding even while taking duphaston,,kindly let me kow..