I Have Had A Solid Raiseditchy Rash For 2 Days

I have had a solid raiseditchy rash for 2 days with no fever before or since that completely goes away whin I take benadryl, however after 4 to 6 hours after taking the benadryl the rash returns with vengeance. I have not changed any of my habits or food other than consuming salad more often than usual.