If you've ever had chicken pox, then that sounds like it could be shingles. You should get it looked at asap, and keep it covered and wash your hands really well if you touch it until you can get it looked at.
Have you had chicken pox in the past?
It sounds like it could be, but just a guess. You should see a dr. to find out for sure. I have pain under my rib, but it tourned out to be a condition called costochondritis. Inflammation of the rib cartalidge. Bit no sores. Def, check with the dr. so you can be treated and heal. Best of luck.