A couple years ago I ended up in the hospital for 10 days on IV antibiotics and morphine because of an infection. I started with some pain twinges in one of my teeth. It got a little worse so I went to my dentist. He did x-rays and checked it out and said everything looked fine. BTW I love my dentist and he's very competent. There really was nothing that showed on the films.
I started getting waves of pain a few days later so went to urgent care. They checked me out and said it must be a TMJ problem. Try more Advil, hot washcloth packs and see a TMJ specialist. Ok, I did all that and made appt to see Oral Max. surgeon (3 week wait).
The following weekend the pain came in more frequent and EXCRUCIATING waves. I called the dentist on Saturday and he said, to start on amoxicillian and see him on Monday. OK, lots of Advil kept me going but still uncomfortable.
Sunday, I decided I just couldn't wait till Monday so I went to urgent care again hoping to at least get something more for the pain. They did about a 30 second exam and said to drive straight to the ER. They called ahead and had the on-call ENT there ready. I was admitted immediately and they thought I had an infected salivary gland and maybe a tumor on that gland. They did CAT scans, etc. Basically kept me on pain meds and STRONG antibiotics 24x7 for the 10 days. They ruled out cancer but were still worried that the infection would spread into my brain.
It turned out to be cause by my bottom left molar that was infected and needed a root canal and crown.
My recommendation would be to get it checked out.