I went through the exact same thing.. for me it meant pred wasn't working anymore (they stop using this as a treatment for me) Plus with the arthritis. I suggest you get off of it before it gets worse, speak with the doc about another med. have you consider remicade, or humira? Remicade was wonderus for me until I got the antibodies from it now I suffer hard core athritis (to the point it's deforming my body) now back in Imuran and waiting to start humira. They say this med is allot better to keeping you cd under control for allot longer then remicade. and really suppose to help with arthritis (taking Imuran at the same time tho)
I hope for you it's nothing more then that. I hope it works out for you, and the pred caused no more painful side effects.