My Scalp Looks Like It Has Been Sunburned While I

My scalp looks like it has been sunburned while I have not been in the sun. This just developed about 6 weeks ago and I have tried changing shampoos to no avail. Could it be drug related? The texture of my hair has changed and am losing some. I did have radioactive iodine a year and a half ago following thyroid removal due to cancer.