Oh my gosh. This is the EXACT same thing that has just happened to me. I am 33 and have never been allergic to anything either. I just completed my first round of prednizone and am going back to the dermatologist tomorrow in hppes of figuring out what is going on. My rash came back after about 5 days after I quit taking the medication and like yours, when it returned, it spread up my thigh and is now on my arms. I'm so worried that I will have this for the rest of my life. :-(
Can anyone advise please?!? Thanks!