Skin rashes for my toddler

pHi there,

I am hoping someone could help me. I am at my ends meet with my 2 yr old son. I feel so bad for him. He is constantly itchy and irritable due to a rash/hives that break out all throughout his body.

The rash starts red and it feels sandy, bumpy and dry. It comes in patches all thorughout his body after the redness goes away it leaves the skin discolored. The worst parts are behind his knees, arms and specially the top of his feet, This area gets really red, and super dry and scaley, he scratches to the point he bleeds and it seemed to not help it. I keep his feet covered. I have tried almost everything I can find over the counter to help with cracked skin and itching. petrolium Jelly seemed to help with the cracking and scaley skin.

His back and neck are now starting to get the redness and it feels sandy to the touch.

I also forgot to mention I have cut all gluten out of his diet and it helped for a little while but it is still hapenning.
his cheeks get red everytime he eats and his rash worsens during a bath or shower, or if he gets hot and at night.

It just seems like everything effects it and I dont even know what else to give him. I tried the medecine finder tool and it came up with sulphur.

What dosage should I give him and what can I try to give him if that is not it.?

I want to thank you for your time and if anyone helps me thank you so much in advance.