I was also on progesterone during my first trimester and am still on metformin. And I totally agree with what you've already said...quit charting, it really isn't accurate once you have a positive prego test. My bbt plummeted on day 26 of my cycle and I thought it hadn't happened, but it flew back up the next day and now here I am 27 weeks pregnant (after seven years of infertility treatment and not a single BFP before this one).
Thoughts and prayers--hope you have a wonderful pregnancy. =)