I believe the slow tanning is from low levels of the amino acid L-Tyrosine, which is a non-essential amino acid made by the body.
I made this connection a few years ago. A doctor recommended Tyrosine to me, I believe for energy. It gave me very bad anxiety, so I stopped. I think it was too stimulating, which is probably why the body makes less of it for AF.
Anyhow, when researching Tyrosine, I found it is needed for tanning.
So....I think the body makes less Tyrosine, since AFers can't handle it, which leads to reduced tanning.
If you are not sweating, that makes heat intolerance bad because your body can't cool itself. I had this for several years.
If you stay in the shade, it might not be too bad for you.
Maybe just read a book in the shade, go in the water once in a while to cool down. Try to minimize direct sun.