Why Am I Having No Menses After Taking Duphaston?

i have pcos my doctor prescribed duphaston 10mg BID for 10 days together with metformin 500mg TID. I started taking duphaston first week of May but up till now i still don't have my period. Usually when I take duphaston i have my period within 7 days. I checked with home pregnancy test 2 weeks after my last tab of duphaston and it was negative. I went to my doctor and told me just to wait. Its been more than a month already but still got no period.