Suggest Treatment For High Fever And Blisters In A Child

My name is shawntay brasher I have my 2 yr old son at the er last night because he is running a 105 fever and red blotchy blister looking bumps all over his body. They said they think it s a viral rash but I think it has something to do with a tick bite he got 3 weeks ago that bulls eyed. The symptoms are getting worse the rash is starting to get a blackish purplish center.. should I take him back to hospital or do I just wait it out. I have pictures if I can send you one?