You appear to have urticaria, or hives. Most hives are not allergic. If the hives come exclusively after scratching, they are called "dermographism" (skin writing). The cause of these is usually not known, but is hardly ever soaps and detergents or diet, despite what you hear people say. The hives can last a few weeks or a few months, but then go away. I suggest you set up a doctor's appointment, and while you're waiting, take a Claritin 10 milligram tablet every day (an antihistamine) and apply Sarna lotion or Benadryl cream as often as needed to help the itch. Both these products are over-the-counter.
Best.
Dr. Rockoff
Dr. Rockoff