M.K.
My son wore a DOC band for 4 months. We were told only to use rubbing alcohol to clean it. Put it on a wash cloth and scrub it once a day.
I was also told not to use any creams on his head. The kids sweat in it no matter what you do, so the creams along with the sweat will break down the skin causing the itching.
I would call the place where you got the band and ask them for help. After 3 weeks your son should not be having a issue with a rash.
Good Luck!