Suggest Treatment For Neon Red Hives On Body

I woke up yesterday covered in neon red hives. thinking I was having an allergic reaction, I took some benadryl and went back to sleep. When I woke up, all of my joints were twice their size and swollen. It hurts to move. I went to the hospital, they said I had reiters syndrome, and put me on microbid and 50mg of prednisone for the next 5 days. I woke up again today covered in hives, and I can't find anything online that mentions hives as a symptom of reactive arthritis. is there something I dont know? I'm kind of panicked.