Hi Mushloom,
My son is heaty and get rash easily too. I brought him to the dermatologist. Doctor advised not to bathe him too often, use non soap cleanser example Centapil, Sebamed and need lots of moisturing and the water should not be too hot. I tried many moisturiser and found that California Baby's Calendula cream works very well. Dr prescripted steroid cream, Elomet, to my son. I only apply on the body and used Calendula Cream on the face. Now, it is clear. I use the Calendula cream 4 times a day when he has the rash. Try to wear 100% cotton as well. Dr told me that babies will grow out of it.