What Causes Recurring Itchy Rash?

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I have a rash that appeared about two months ago and has just reappeared, the only difference is that for the past two months I used tampons when starting my menstrual cycle, also my lower back has been hurting since this occurred also, on a doctors visit I had blood in my urine and after a retest the urine was negative for blood this rash I have is very fine, no redness, just very very itchy