Progesterone?

I had a miscarrige at 15 weeks.
My doctor took blood, and ran some tests because we weren’t sure why i had a miscarrige… i’m the one doing my iron tests once a week, and taking iron pills+prenatal vitamins+ following a “diet” set forth by my doctor— i honestly did everything right.

low iron, 14% white blood cell count, and low progesterone…
okay, i get iron and needing white blood cells… but what does progesterone have to do with the pregnancy? and how did somehow… my body not make enough?