Advice needed about rash?

https://preview.redd.it/kds7ggsf9y6g1.jpg?width=3024&format=pjpg&auto=webp&s=ebe015732a81d2f284ea2867d0e730fcc8af3a5a

this is a non blanching rash. will be speaking to his GP about this but just wanted to see if anyone had any ideas? I think it could be heat rash. We wash with sensitive laundry detergents, wash him with no soap or fragrance free soap and don’t wear perfumes or have strong fragrance in the house etc etc. Only 5 and a half weeks old. thanks!