Heat rash?

Some of you may have read my post about my 3yo being tested for Celiac Disease, but if not here’s a short explanation.. he had problems with constipation from 6mo to almost 2yo then problems with diarrhea from then to about 2.5. From then until yesterday he pooped mud every 4-6 days and screams and cries and it’s a big deal on poop day. He pooped last night- mud. This morning he woke up with diarrhea- pure liquid. He laid down for a nap and woke up freaking out because he had an accident.. he NEVER has accidents. It’s pure mucus, like snot/jello and smells SO bad (always smells terrible) I talked to his dr and he just said make sure he stays cool (he’s spent the majority of the day in a cool bath, and in front of a fan plus its pretty cool in my apartment. The whole point of this is, the dr asked if he had a rash, he just had a very red splotchy face but now this is what he looks like.. does it look like heat rash or an actual rash? He’s in so much pain when he has to poop and NEVER goes this much and his doctor just keeps saying “keep him cool, give him fluids” “we’re talking about Toby right?!” Like wtf, I specifically texted and said “I need someone to call me about Toby please” 🤦‍♀️