You could also be having a shingles flare.

If you have had chickenpox as a child, this virus is capable of coming back and causing severe pain. You will not necessarily get a set of blisters with it.

A doctor can run blood titres of the zoster antibody and find
very high levels and perhaps try an antiviral on you.

This is a very misunderstood presentation of Herpes Zoster, but it can happen. A diet high in arginine may trigger it since the virus uses arginine to replicate, or stress or a lowered immune system. I had shingles on my right upper arm when I worked midnights, and it flares now and then. Less now, after 10 years, however.

Something like this that goes away and comes back should be looked at with some blood work.

Here is a list of foods that are high in arginine. To reduce the impact of arginine, taking some l-lysine will mute the virus to some extent..but it is not a cure. The ratio of l-lysine/arginine is thought to be a trigger for Herpes viruses.
http://www.herpes.com/Nutrition.shtml