Sorry I meant rast testing n also sorry in advice if I sound rather "noob" ish its because I never dealt with allergies as a kid they really only have been interfering with my quality of life for a short time now n I know nothing about the different tests n how it works n stuff :p
Hello and hope you are doing well.
With Dermatographism, it may be difficult to detect what you are allergic to, hence your doctor would have tried ruling out food allergies. Scratching the skin will trigger reactions. Unfortunately, there is no cure for dermatographism. Treatment involves trying to limit exposure of the skin to the triggering factors. You can monitor to see what is triggering your reactions, dust, changes in weather etc. You can try avoiding the triggers and also you can try to refrain from scratching yourself. Anti-histamine medications may be of some benefit. If taken regularly, they can help to reduce the severity of the skin reaction. I suggest you discuss the treatment options with al allergist.
Hope this helped and do keep us posted.