I Have Been On Levothyroxine For A Few Years And

I have been on levothyroxine for a few years and have been suffering from what I think is a reaction in the form of a rash. It itches non stop. It started on the back of my head and now I have it all over my arms, legs, and back. My doctor tells me that there is nothing that can be done, but certainly there must be. Please help!