What Causes A Raised Itchy Spot On The Back?

I have a raised spot on my back (not a spot but a small round raised pimple) it is really itchy but it hurts to touch. It feels quite num to the touch but soon hurts if i itch it. The skin around it is abit red and dry so i presumed it would develop into a rash but it hasnt, it has just stayed at the one pimple for nearly a month. Iv had shingles before and wondered if i was getting it again but it hasnt developed into that either! Just wondering if i should get it checked out or not?