Has anyone ever had an allergic rash for a month and it went away for no reason?

Hives come and go... Hives, medically called urticaria, often a result of allergy but actually cause is difficult to find. Some people have hives for few hours, others come/go for days/weeks/months or even years then disappear just as mysteriously as they come. As mentioned, the search for cause is often illusive. Zyrtec/claritin/allegra/benadryl often help. Consult your doc if you are concerned. Good luc.