What Causes Sore Rashes On The Skin?

it started out looking like little bug bites on the right side of my abdomen but now it looks like it could be contact dermatitis except it has started to spread. The skin around it is sore to the touch like a bad sunburn. I also feels like I have a bad sunburn on the underside of my right arm except it is not sunburned. I am 17 years old and 155 pounds. I have been nowhere near poison ivy or anything that i may be allergic to.