Rash is getting worse

I have had this rash since I was about 15 and am now 19 almost 20, Ive been to the doctor many times and have been diagnosed with different things each time, the last decision was that I was allergic to Nickel and the buttons on my jeans were causing this rash, well the rash which I know was from Nickel has gone away, but the other rash which they told me was my bodys natural reaction to the nickel caused rash is still here, and it comes and goes. I have no clue what it is but this time it doesnt seem to be going away and is spreading. It itches very badly, ive tried benadryl, aveeno oatmeal baths, and cortizone and nothing seems to work. If someone can figure this out for me Id greatly appreciate it!! Please post any suggestions or ideas. oh and just so you know, the rash is on my sides, back, arms, legs, stomach, and neck, it seems to be symmetrical but im not sure.