Poor baby

My poor son (3yrs old) has a bad rash covering his entire body. It started as a rash on his bottom and we thought it was just a diaper rash, so we treated for diaper rash. It didn't go away, so we thought maybe a heat rash. We let him run around naked for a little while each day. That didn't help, then the rash started to spread. (By this time he's had it almost 2 weeks) So I took him to the doctor and they said it's a yeast infection and that the rest of the rash is a reaction that the body has after having an infection too long. Well, that was last week on Tues. so we've been treating with Nystatin since three times daily and the rash on his bottom is clearing up. But the rash everywhere else is getting worse, much worse and my poor little fella is just clawing away. Even with me giving him Benadryl. Still not getting better just worse, so I took him to the doctor today again. His normal doctor was in the office today (His pediatrician is part of a group practice) and he saw him and said he's almost completely positive that the other doctor was right, but he wrote a prescription for Claritin to help with the itching and is referring my son to a specialist. Somehow that doesn't seem to me like he's very sure as to the fact that it's just a reaction to the yeast infection that my son has. I dunno, maybe it's just me. I just know that seeing my poor little man running around covered head to toe with this horrible rash is breaking my heart esp. since I know it's bothering him. He's almost constantly scratching even with taking the Benadryl, I really hope they can get us into the dermatologist soon, or that it goes away. I just feel so bad for my baby.