Thanks for the question. There are many potential explanations, so I recommend that you speak with your doctor
. While it could be many different things, your description at least brings into question the possibility of this being an activation of a latent herpes zoster infection. Herpes zoster is the virus that is involved in causing chicken pox, and is the same virus that goes on in later years to cause shingles, as it is commonly known. It does this by residing in a latent form in various parts of the nervous system. Then, often years or decades later and often in the setting of something that causes decreased immune function (such as another infection, advanced age, or even just something as simple as stress), the virus will become active again and cause severe pain. Often, the pain is described in a fashion similar to what you have described, and almost always there is no obvious visible reason why the pain is present--at least at first. Then, over a course of weeks, the skin in the affected area will begin to demonstrate some changes that can be used to confirm that a shingles outbreak is ongoing. There are many other potential explanations for your problem, and so you should speak with your doctor about this.