I took Imuran for a few months, but started to feel pretty terrible. It made me extremely nauseous and hung-over feeling in the mornings. My Dr. suggested I try taking it at a different time, but I tried everything and still felt sick. I also always had extremely dark urine upon waking, and eventually started getting kidney stones, which aren't directly be linked to the Imuran, but they did stop forming once I went off of it.
I switched to 6MP, which is supposed to be easier on your system as it is metabolized version of Imuran. I still feel slightly unwell in the mornings, but nothing so severe as when I was on Imuran. I hope I am not scaring you off of Imuran, this was just my personal experience with it. Apart from the blisters on your chest, I have experienced all of the other symptoms you have from both inflammation, and as side effects of Prednisone. Hope you start to feel better soon, and that you find the right mix of medications that help you. All the best