Dr. Rynne, I Am Experiencing Sudden Pain In The Skin

Dr. Rynne, I am experiencing sudden pain in the skin in my back. I will be sitting here and all of a sudden I get a "zinger". It is very painful and occurs a few times and then stops for a while. It is not internal, it is on my skin. There is nothing on my skin to suggest anything. Earlier, there was a little redness but nothing alarming. Do you know why this might be?