What Causes Red Scaly Rash On Inner Thigh?

Hello, my son has had a rash on his inner thighs for more than a month...it is red, scaly, and will not heal, even with daily treatment with zinc oxide applications. The pediatrician said it looks like contact dermatitis, though no changes have been made in diet or clothes detergent, etc. He has also had persistent mild stomach upset, just enough to curb his appetite slighty for the past month. Now the rash is on the back crease of his knees and is very red (looks like what I had on my inner elbows with scarlet fever as a child.) I am wondering if there is a bigger picture here or if these are separate unrelated issues. Thank you.