Erythema AC rash on legs

I have been getting increasingly severe itchy rashes that start as dots and radiate to almost the size of my hand on the backs of my lower legs for 4 years and was last year diagnosed with Erythema Annulare Centrifugum. Problem is the doctor said that there is no known cause and gave me an ointment (Diprosone OV) to help. It doesn't seem to ward off the rash but it does seem to assist it slightly when it appears which takes up to 3 wks to go away. It's so itchy and has raised bubble like areas on the edges as it spreads radially and darkens from the centre as it heals but I want to rid myself of this rash once & for all and am appealing to anyone that can help me figure out what is causing it.
I eat healthy, am not overweight and am careful with what products I use (soap free etc) on my body.