Hi ladies... new here and I need some help with progesterone

I am 31 and we are currently ttc baby #2. Last time, it seemed do easy. Got.put on metformin, had 1 cycle, then bam! Preggo... this time not so much. I'm still on metformin. .. at same weight as last time, but nothing yet. I typically have a 31 day cycle and docs have been doing 21 day progesterone checks. My first was 12 then 9n now 3.5. Docs are saying I'm ovulating but why are they lower ? I'm a little concerned and quite frustrated that they haven't done any additional hormone testing. Any advice? Thanks