I Have A Rash That Appears For Approx A Week

i have a rash that appears for approx a week then goes away. then returns, it was on both sides of my body and it went away, then it was on my forearm & went away after a week. Now it is on my neck, it is uncomforatble and visable. I have been to my a walk in medical center and they thought it was shingles. I also went top my Dr. and a dermatoligist, he says it is bug bites? I do not believe it is bug bites. It looks like poison ivy. Do you have any idea what else it could be? thanks George