It could have to do with the production of the primary sex hormone, estradiol, and progesterone, which helps regulate your menstrual cycle and peaks toward the beginning of menstruation.
When you’re menstruating, your estrogen level is at its lowest, but you have high “T” – testosterone. This hormone is strongly linked to sex drive in females, who get an extra shot of T during ovulation (aka “mid-cycle”). Basically, it’s just your mom nagging - Mother Nature, that is - giving you a heads up that it’s a great time to make a baby.