Tricia,
Good advice from Elaine, I also would think either herceptin or Tykerb right now would be a good idea rather than nothing at all.
It seems like the Gemzar is not suiting you so either of the above drugs may help while this rash clears up, has your onc given you anything to help that along?
I really am so sorry you have this, my Mum used to swear by Calamine lotion for any type of skin rash or itch but it may be under a different name in the U.S but hoping you find some relief soon.
Sending lots of good wishes to you my friend! xx
P.S I just googled this and it seems you're not alone
http://drugspedia.net/prep/33785.html Its advised to contact your onc about this to get something to help!