Suggest Treatment For Poison Oak Reaction With Sore Throat And Fever

my grandson is 25 developed a very serious rash which travelled all over his body and in his eyes and throat which felt like his throat was closing. He went to ER and they treated it as possible poison oak and put him on presidone for 10 days, now few days after taking the last presidone he developed serious sore throat and high temp. went to er again they gave him vicotin and anitbotic on a friday and by sunday he was back in er with very high temp., they kept him over night and he tested negative for mono and strep but they said it was a virus that could last 3-4 weeks a sister to mono what is it