I’m sorry, but there is no special bonus for the guy with the most problems;-)
Sounds like you already did a lot of investigation. Good that your docs didn’t find any underlying issue.
What comes to my mind is:
– fluid- and electrolyte balance. Are you drinking enough? Or too much? Do you get enough minerals? How much do you sweat?
– if you are a big guy that could be a problem. Especially if comparing to smaller persons
– heat is something the body can adapt to:
You can adapt to the heat, that’s for sure. But it’s hard for me to guess any specific reason for your problem. Especially, if you already saw an endocrinologist.
Maybe my suggestions can lead in a direction, or you find something useful in the article?!
But the most important thing against the heat is a cold Tegernseer;-)