You are not alone Lalobear. I too have worse symptoms on rainy days. Even before I had full blown AF I used to get headaches and feel less energetic. I think it does have something to do with vitamin D, but more so the change in atmospheric pressure that affects our bodies. And we with AF are already soooo sensitive.
I also attribute it to my candida coming out to play. The little b'stards just love a damp and soggy environment. And living in Florida I sometimes feel like a poor old salmon with one fin and half a tail trying to swim upstream when it comes to that issue.

Lalobear- I can relate to this. I love sunshine and warm weather. Really lifts the spirits.

On the other hand there is nothing like taking a nap on a rainy day.

I'm going through this, too. I moved to a sunny climate for that very reason. It's very debilitating to me to be around a gloomy climate.