Originally, I want to finish all 199 pages before joining your topic. But can't wait because you are just talking about what I face in these few days!
Last week my son got serious 濕疹, & then many red spots on his back after sweating a lot last Friday. I also don't know that's 濕疹 or 熱痱, but now I think is 熱痱! His scratch a lot with blood & wounds. Then I brought him to doctor who said is serious 皮膚敏感. Nothing special he ate, so don't know why, just doubt is due to sweating a lot?!
Then doctor gave him some 敏感藥, saying can reduce itching feeling --> that's really work! And some dark brown watery stuff for bathing, I think it's 皮'tak'露 which he tried before. He's better now but still got some red spot on back. When you touch his back, it's rough also. Is that similar to your baby? Is 熱痱 rough?
Sorry, I don't have Chinese software (but can read Chinese), so need to write in English with some Chinese word copy & paste from other websites.