Interestingly, my mom has been experiencing something like what you're describing since COVID as well, she gets a badly swollen calf and ankle with angry red blistering rash. She is prescribed prednisone cream which seems to work for her, but it doesn't keep in from flaring up again some other time, perhaps when her immune system is run down. Doctor says it's from COVID and they see it all the time now. It's different from the EM I experience in that it is an obvious rash, but it's similar in that there is a lot of pain and heat. So strange! There needs to be more support for all these weird symptoms of Long Covid.