How To Get Rid Of Skin Rash On Shoulder ?

Hello, my name is Andrew. I m 18 and I recently noticed a rash on my shoulder that is near my armpit area. It is just beside the beginning of my bust and it is red and looks kinda like a cigarette burn. I also noticed some dry skin patches that don t hurt and aren t too noticeable that are almost symmetrical with the first rash. These aren t red or burn-like. I ve had dry skin pretty much my whole life due to the dry climate (Las Vegas) . I am afraid that it could be something bad. I had a blood and urine test in August and was told I was completely healthy. I m sexually active, but haven t had sex in a few weeks and plan being away from sex for awhile. Again, these just recently showed up. I don t know if its from dirt, sweat, allergies or even a possible HIV , but I need help because I m terrified. I don t think it s HIV because I haven t had any other symptoms of it besides a rash. Also I read on a blog that this woman had the same exact thing as I have described and she said that she found out she was allergic to wheat. So if you can help me that would be greatly appreciated. Thank you.