If one of your teeth feels extremely sore or you’re experiencing a constant, throbbing pain, it’s most likely the result of an infection in or near the tooth. Other signs of a dental infection include:
Chronic bad breath
A persistently bitter taste in your mouth
A feeling that one or more of your teeth are loose
Swollen or red gums
Sensitivity in a specific tooth
A draining sore on the gums near the hurting tooth
The only way to know for sure whether your toothache is caused by an infection is to have a dentist take a close look at it and capture X-rays.