Brain fog and hormones.

Absolutely. This has been more of an issue since moving further toward perimenopause. My progesterone take longer than it used to to rebound after my period, so for a week or two I feel terrible - low energy, depressed, foggy, headache. For over a year, I just assumed I was very anemic, but aggressive supplementation didn't help, and blood work never showed anemia, so I figured out it was hormonal. Vitex and progesterone cream (Karuna) have been helpful, but only to a degree.

Keeping a calendar is a good idea, but it's also not foolproof because hormones don't follow a set pattern, and can be imbalanced in different ways, at different times, in the disarray of perimenopause. Like one cycle you might have estrogen dominance symptoms, the next be low in both estrogen and progesterone, and the next feel more or less fine. So it's very difficult to tell if a remedy is helpful or not, too! So frustrating.

I highly recommend the Heather Corrina book What Fresh hell Is This? and Lara Briden's blog. The latter has a helpful post about how histamine and estrogen interact to activate mast cells, which also causes brain fog, especially for people with chronic illnesses that predispose them to mast cell activation syndrome. https://www.larabriden.com/the-curious-link-between-estrogen-and-histamine-intolerance/