Upper Arm Rash

Hello I have been meaning to post on a forum like this for quite a while now. I have had a rash on my upper arm and shoulder area for well over 6years now, it used to be just under where my t-shirt was on my arm so my family tried changing laundry soaps not using fabric softener anything I could think of. With all the new laundry soap these days that are hypoallergenic I thought some would work but still nothing. I went to a doctor when I was younger about this and he gave me a cream and it did nothing. The rash went dormant for a while only showing up in the summer,  then all my family started saying " o it's just a heat rash ". The past year or so  the rash has come back but on a permanent basis but now it is alot more red and has a bigger area of my arm covered, it can no longer be covered by a t-shirt, and even worse it has begun to itch frequently. So I went to my new doctor a couple months ago and he just took a quick glance at it and gave me another cream. No dice! I am about ready to go to a dermatologist but not sure what they charge even for a diagnosis. If anyone with a little more knowledge could point to something a little more insightful then my run in the mill family doctor your help would be enormously helpful and would put years of discomfort to rest (possibly). Thanks for your time and making what seems to be such a helpful communitee!