Hi, I just wanted to toss in that you can have RA and your x-rays will look normal...I had x-rays a few months back of my hands and they were normal, and I commented to my doctor that I didn't understand how my hands couldn't hurt so much and have my x-rays normal, and he said inflammation doesn't show up on them, only joint damage...it can take YEARS to get damage from RA.
Also, sitting usually makes it worse, at least in my hips. When I get up..ouch! and I'm stiff for a bit while walking around..
All of my tests have always been normal and I have been going to the same rheumy for 4 years now, for what I thought was some kind of reactive arthritis 
Although, I do have to say for joint inflammation pred is usually the gold standard because it is what usually works, I can clean my entire house on about 10 mg of pred. I feel like super woman, that is the only medication I have ever taken that made me feel almost human. Do you think it is fibro? I think someone mentioned to me once that if the pred/medrol doesn't work then the joint pain could be fibro related.
How long have you been taking the Plaquenil? That worked for me too, and if you keep taking it, over 3 plus months you will see a difference but don't keep starting and stopping it. I did that a few times because I thought I didn't need it and it took about four days and I couldn't get up my stairs. Although, make sure you get a baseline eye exam for plaquenil users, I had to stop mine because it became toxic for my eyes. I didn't get the baseline so we aren't really sure how long it was really affecting me.
I know it is frustrating, have you thought about getting a second opinion? You don't need positive tests to recieve treatment.