How To Get Rid Of Rashes All Over The Body?

Good day, my son has had a rash for about 1 1/2 weeks now, he has been seen by 3 doctors and no one seems to know what it could be. He is more tired than usual and had a fever running after 1 week 4 nights in a row (at night only). It is very itchy and the breakout is all over his body exept his head, the rash is not red, it's like goosebumps all over his body even on his toes and fingers all over his face, no one knows what it could be, his appetite has decreased as well... help!