Severe Poison Ivy Rash and Crippling Knee Pain

I have a very bad case of Poison Ivy.I went to the ER 3 times and at first they thought it was a ringworm.However , different doctors and my family care physician told me it's Poison I've.Any way .I was prescribed Prednisone ,which is a oral and cre medication.At one point the doctor from the ER told me to stop taking it because it was making it worse .Anyway ,I'm back on it after abruptly stopping,and instead of the 10 mg that is a normal dose ,I'm on 40 mg now mind you after abruptly stopping for a week .The rash is really bad and extended to my belly and it's on my forearm.The problem is from 2 days ago ,I'm experiencing the worst knee pain you can imagine.Both my knees feel like there's a sharp throbbing pain in both my knees ,Soo painful it's crippling and extremely scary .I've never experienced anything like this because.I called my doctor and left him a message.In the mean time ,I'm trying to take it easy and educate myself and see if I could just stop taking it because of the crippling pain .It's unbearable.Like something is electrocuting me .Plz any advice would be greatly appreciated.God Bless !