There are allergies that are within; my "skin" organ is susceptible to rashes and hives, etc. I do inside out sensitivities unrelated to location as well as contact dermatitis. It was 4-5 years ago that I figured out the rash I'd had on my leg since I was 13 was because I was "allergic" to my cat(s)! I was, for the first time that I was paying attention, without a cat and the rash went away and then a couple years after getting my two I have now -- though I don't sneeze or have any "usual" allergic responses, the rash is back :-) Too, I've just gotten back my occasional dramatic neck hives that have been gone since my last cat died 6 years ago (and I've had these two critters for 5 years). But only the rash is consistent and there all the time but it's on my inside calf and my cats don't ever get there :-)

Were I you, I'd look at EVERYTHING that changed up to a year before the rash? Does it itch consistently, the same itch or are there variations in how bad the itch is, etc.? Are you taking any different meds from before the itch; might be an inert substance in them that you're allergic to; those things aren't on the bottle :-) the taste maskers (my husband invested in a pharmaceutical company that specialized in medicine taste maskers; who would have thought there was such a thing?) I have never seen a rash that "disappeared" when you did anything to it? Are you just "blotchy" or do you actually have raised bumps? I'm worse at night when I'm trying to go to sleep, I guess because I'm settled and not distracted at all/doing anything.

Did you see this site with 326 medical conditions causing rash:

http://www.wrongdiagnosis.com/symptoms/rash/causes.htm