Suggest Treatment For Itching After Sun Exposure

I have dermographism. I enjoy being outside during the warm summer days but for the past 2 days, I have found I am itchier than usual. It the sun exposure making my condition worse?
I am a 47 year old woman who got this condition earlier this year. i am in otherwise perfect health. I have been tested by an allergist and found I am not allergic to anything.