Hi... I Am 35yrs Old Had A Successful Tubal Reversal

Hi... I am 35yrs old had a successful tubal reversal but now have problems w my progesterone being low. My dr put me on metformin and i usually have a cycle 25-28 days monthly but last month i had a 2day light period (which its normally 4days and heavy) july 14&15. This month august 9 i saw blood when i wiped i thought i was about to start put a pad.. And nothing. Aug 10th no blood august 11th again only when I wipe. Could it be the metformin? I haven't done pg test because I have had many negatives in the past so I don't want to get my hopes up. Please help..