Welcome and thanks for posting your query to HCM.
It seems that you are suffering from the problem of Dermographism- which is a type of urticaria
where there is appearance of temporary evanescent swelling of skin with itching over the line of trauma, rubbing or scratching. This is a common entity and not as all a serious problem.
The most important thing to prevent it is by avoiding scratching and taking round the clock antihistaminic drugs. The best would be non sedating antihistamine such as Loratadine
( can be taken up to 1 time or can be increased to 3 times a day) or Fexofenadine
( single dose).
Do not be panicky about the situation as it is simple hypersensitivity
where most of the times we are not able to find a particular cause and is also self subsiding.
Hope this information will help you.
Dr Sanjay K Kanodia