Heat and sun-related undiagnosed health condition

The story of Nathalie

I was born in a hot country and lived in hot countries until I was in my late twenties.Ever since I can remember, though, I’ve always hated the heat and the sun because of how they make me feel.
I’ve now lived in the UK for the past 12 years and what started decades ago has now worsened. Here is a list of my symptoms below if I’m exposed to a hot environment (which my body thinks is anything above 18 degrees) or have to be in the sun:
-rash on skin in spite of wearing a factor 50 cream within minutes
– burning sensation on skin
– bone pain especially in joints and limbe
– palpitations
– difficulty breathing
– nausea
– severe headache
– dizziness
– eventually fainting

I have never met anyone who fully understands my condition and doctors have carried out a number of tests for the past few years which have all come back negative.

Has anyone ever experienced this?