Okay. So, to review, you have a single sore tooth, no swelling or inflammation, no recent cavities filled or crowns placed, and you don't grind your teeth.
In this situation, the most likely explanation is a cavity, a cracked tooth or an old, cracked filling. An injury to the tooth could also be to blame. For example, an old sports injury could have injured the tooth, its nerve, or its blood supply so that over time, the tooth becomes more sensitive.
See your dentist. Treatment is generally quite effective!
Just one more question. Do you take a medication for osteoporosis or other bone disease, such as alendronate (Fosamax), risedronate (Actonel), ibandronate (Boniva), or the intravenous medication zoledronic acid (Zometa or Reclast)?