I had a very, very bad rash after dd was born. It was never diagnosed as PUPPPS. My doc didn't know what the rash was. Both of my legs were covered from my feet to my upper thighs with this awful rash. I remember laying awake at night itching my legs so much, it would wake DH. While I have no experience with predisone, I can tell you that the only thing over the counter that worked for me was Cetaphil cream. It saved my sanity and allowed me to get some sleep.
"When you come to the end of your rope, tie a knot and hang on."
~Franklin D. Roosevelt