Hives and thyroid cancer

I have thyroid cancer and just had my thyroid removed in 1/09.  I was put on cytomel as a temporary drug until I started treatment with radioactive iodine.  I went off of the cytomel (no other thyroid replacement drugs were being used) and on the third day I broke out in hives all over my body.  Benedryl had no effect on the hives for days.  Finally I was put on steroids while being hypothyroid.  Is this safe?  The steroids have not cleared up the hives, but they have relieved some of the itching.  They want to keep me on a high dose as I am doing the RAI.   Is that ok?  Could it be possible that the hives will just go away once my TSH levels go up after the RAI?