What Causes Sudden Onset Of Welts On Chest And Back?

I have sudden onset 20 or so welts on my upper Right side of my chest and on my back. A few on my neck and on my chin. I also have a slight sensitivity to the right top side of my head when I lay down on a pillow or on the car head rest. Right ear hurts slightly. Also a slight right sided headache. Am 50 y/o. Had a recent upper resp. chest cold. No markings on the left, no sensitivities on the left side of body. What may this me?