Suggest Treatment For Persistent Rash On Neck

Hi i have had a rash that has been reappearing on my neck for the last 18 months and for the last few months now appeared on my forehead. It does not itch, nor is it sore. It first appears as small pimple like spots which spread outwards and then eventually disappear on there own after 2-3 weeks with no treatment. I have made several trips to the doctors who advised it is an allergy, but im not so sure. I have tried every cream, lotion and potion going and none have helped. really getting me down now please help.