What Leads To Itchiness Of Skin Post Bone Marrow Transplant?

I have received a bone marrow transplant 11 months ago. 6 months later I began experiencing unusual itchy skin. I had blood work done and was dx with gvhd of the liver. I was placed back on prograf in sept. and am currently down to 5mg once a day every other day of prednisone. Now the unusual itchy skin has returned. Have you ever heard of unusual itchy skin that has no physical signs of rash or anything?