How To Get Rid Of Skin Allergy?

Hi doctor,
Kindly inform me exact answer about the problem I have and what I have to do:
" I'm 26 years old man. I'm student and suffer from akin allergy for about 8 month and I did blood test my doctor told me that my blood safe. however, I have these symptoms: all my body scratching me and I can write any thing on my skin using my finger, I mean when I touch any place it becomes red line and it continue until 25 minute" my doctor told me it is Dermographesim. and I'm using these medicine for a long time with out any benefit I think it is just for hiding my allergy (Fexofenadine Hydrochloride, Ranitidine 150mg, Loratadine 10mg , Levocetirizine dihydrochloride and some others) when I use medicine I fell better after one day if i do not use medicine it comes back again.
If you want me I can send you my body pictures to see it?
please inform me exact answer
many thanks
Rebaz"