Suggest Treatment For A Blotchy Rash All Over The Body

My son had an upper respiratory cold with double ear ache. He was put on Albumen. 8-9 days later he broke out in an itchy rash. I took him to the doctors and they switched antibiotics and gave him benadryl. The next day he quickly spiked a high fever and then suddenly was unable to stand or even be touched on legs or arms. His joints were swollen and puffy. I took him back to hospital where he stayed the night to be observed. He is feeling much better except he still has a blotchy rash that comes and goes all over his body. He seems to be more hyper than most times also. any suggestion?