Why? help

So I’m 6m PP my periods were pretty normal irregular but normal before baby and a little after baby I always got them around or after 14dpo for the last two months I got them at 11dpo last month and just now at 9dpo why? I do have pcos but this never happened I just started metformin for pre diabetes but it’s only been a week so it can’t be that I’m lost I don’t get it any help or advice is appreciated