Yes, My Husband Has A Bad Rash Since December We

Yes, my husband has a bad rash since December we thought It was poison sumac. The doctor never said what it was but gave him a prescription for pregnazone? . It was pussy and all over red then the itchiness started to relieve itself after 3 wks. NOW it's has welts all over and spread around his stomach to back. The doctor he saw yesterday has no idea what it is do you have any suggestions on what it could be?