A viral infection is the most common cause. A sore throat caused by a virus is most common in the winter and lasts anywhere from 3 to 10 days. This is often followed by a dry cough. The next most common cause is a bacterial infection of the throat. Strep is the most common bacterium, but another bacterium, called Haemophilus influenzae, and even gonorrhea can cause a sore throat.
Bacterial infections tend to cause fever, swollen glands in the neck, and whitened tonsils.
Bacterial infections are treated with antibiotics. Less common causes of a sore throat include inflammation of the thyroid gland and even cancer of the neck or throat. Most of the time a sore throat is viral and will run its course. You can learn a lot about your own sore throat by taking your temperature, feeling for swollen glands, and looking in your throat with a good flashlight and a mirror. Gargling with hot salt water may help a bit.