What Causes Rash On Neck Along With Mild Pain In Shoulder Muscles?

I have a horseshoe shaped rash on my neck. I have not changed anything in my soaps or shampoos. I do not work. So that can t be the cause. I have tried destine diaper cream, Vaseline, triple antibiotic ointment, benadryl, hydrocordizone cream, all to no prevail. The only one I got a reaction from was the triple antibiotic ointment and it was a negative one. It mad it itch were as it has not itched once in the month and a half that it s been there. It has not moved, it has not gotten bigger or smaller, it has gone to a deeper relish color over this time period but that s it. It causes frequent head aches and pain in the back of my neck and down my shoulder and bicep but no further. It does not go down my chest or hurt in any other places. There is a constant dull pain in the neck and shoulder muscle.