Hey Leigh,
I wanted to welcome you to the forum too, and to tell you that I have those blotchy areas on my upper arms, but it seemed related to the sun to me.
And I have the sun sensitivity that you talk about and it does seem to be worse in early spring through late summer. And after a day of being exposed to the sun, I get sick like I have the flu, every time.
Now it seems to be getting worse. Less exposure to the sun is required to make me sick, and sometimes the flu symptoms arrive the same day I am in the sun. And sometimes it is like the sun is just draining all my energy from me. Told my kids I must be part vampire
Hopefully you will get some answers when you have your blood tests done
Hester