question about rash in 12 year old?

son has a rash on his face some spots 5cm x 5cm and looks very inflamed this is also with black stools. We have been to the take care clinic at walgreens for some emergency relief but nothing is working tey gave him a steroid cream to put on the rash, he has had no relief and we need to know what to do. He has eaten no different foods and poison ivy/oak is out of season. Any suggestions would help on how to make him comfortable and make the rash go away he says it burns and is very itchy. We are trying calimine lotion and an anti itch cream like cortisone already. thanks for any help.