I Get A Rash All Over My Torso Extendingto My

I get a rash all over my torso extendingto my thighs and down my arms whenever I don’t feel well. This rash goes away in about three days I have had it biopsies and the dermatologist said it doesn’t suggest anything I currently am an insulin diabetic. I have arthritis and have had my thyroid removed. Don’t know what else you might like to know