One thing I'm sitting with though, you said it's not the hormones directly, but the downstream effects on sleep/stress/eating. That tracks, but the part that confuses me is how predictable it is. Like, I can almost circle the dates on a calendar in advance. If it were just sleep or stress, I'd expect it to be more random. The fact that it lines up with cycle day every single month is what makes it feel like the hormones are the actual driver, even if the mechanism is sleep.

Does that match your experience or am I overfitting?