Progesterone is produced by the corpus luteum after ovulation occurs. The corpus luteum is the follicle that is left over after it releases its egg for ovulation. This means that if you're not ovulating, you will not be producing a corpus luteum, and therefore, progesterone, leading to low progesterone levels.
Progesterone is a female sex hormone that plays an important role as it's the most crucial hormone in the regulation of the menstrual cycle. Also, its main job is to get your uterus ready for pregnancy.