Metformin and late period

Hi ladies,I've been on metformin for a month now my dose is two 500mg pills twice a day . My cycles are usually a mess but for the past 4/5 months it has been quite regular , every 42/45 days but now I'm on cd 55, no sign of my period and negative for lh and hgc test .I was diagnosed with pcos that's why my doctor prescribed metformin to make my cycles shorter and hopefully make me ovulate , I've been ttc for 2 years now .