UGH! poison ivy? how long will it take for it to go away?

I have poison ivy all over my feet and ankles and its spreading all over my chest. I can pretty much feel it forming under my skin EVERYWHERE! I can't sleep and it's so horrible. And i'm supposed to go camping next tuesday!...Yesterday I went to the doctor and i was prescribed Prednisone. I'm on it 3 times a day for 3 days. I've been putting Calamine on it, but it hasn't worked because I have found myself itching the poison ivy in my sleep and just making it spread more. Will the Prednisone make it go away in the 3 day? I haven't noticed anything, but I've only took 2 pills so far...?