hi i have had the same problem for the last 2 n half yrs sometimes its itchy blisters that you want to rip your skin off other times its red patchy rashes all over my thighs.
been to skin clinic and diagnosed an allergic reaction call URTICARIA. unfortunatley there is no treatment other than antihistamines, apparently it starts when you are stressed etc but can stay for 6 wks, mths or yrs. its a pain in the ass.
mine still comes and goes but my skin reacts with warm & cold water well everything really. am clear at the mo but as i say it comes and goes, really sounds like you have the same so if dr says its an allergy this is prob what it is so ask to be reffered to skin clinic. hope this essay helps!