Has anyone experienced something like this?

So I get this from using my tens unit, but only on one side of my lower back. I thought it was not related but it happened again. It can’t be the adhesive bc the rash would be in every place I used it right? It only happens on my lower back on the right side and I’m not even sure if it happens every time I use it…doesn’t itch just hurts. Has anyone experienced something like this?