What Do Red Rashes On The Body Indicate?

I am deciding whether I need to go to hospital ER. I was at ER last night for bad allergic reaction -- unclear what caused it -- which caused difficulty breathing, hives on upper body, hands, back of neck, less on lower body. Breathing improved, swelling went down and hives improved a bit. Was given rx for 20 mg prednisone bid and 2 benadryl every 4 hours. Now a new symptom has appeared and I have no idea if it is related or not. I have an irregular patch of red hot skin around IV site in crook of arm. And I have a bigger streakier hot red patch on my knee. No hives or itching on either of these red patches. I had cellulitis on my outer ear some years ago and it reminds me of that. My doctor gave me the idea that cellulitis is serious. I don t know for sure if this is cellulitis or related to the allergic reaction. What else could these hot red patches be? And do you think I should go to the hospital?