Metformin shortening my luteal phase?

I have been on Metformin for reccurent miscarriage and possible pcos (some symptoms but negative testing) this is my 3rd month and my luteal phase has gotten shorter by 1 day each month til this month when AF came on 11dpo. I am concerned that it is somehow messing up my cycles which were previously long in length at 32-35 days but consistently had a 14 day luteal phase. Has anyone else had this problem?