There are many conditions that can cause a sore throat. Some are minor, and the pain is a direct result of strain or or the environment on the throat, such as sleeping with a draft (the cold air can dry out your throat, but this usually resolves itself a few hours within waking, and is greatly helped by drinking water), or such as the night after screaming at a concert.
However, most of the time if a person is having significant discomfort from a sore throat, the cause is a more serious.
The common cold (rhinovirus)
Colds often begin with a sore throat. Depending on your immune system and the strain of cold that you’ve caught, this sore throat typically lasts between 1-7 days before moving on to the next stage of the cold, which is usually a stuffy nose. Some people report minor pain that is barely an inconvenience, while other people report severe pain that can only be alleviated with medication.
Strep throat
Caused by a bacterial infection, this can result in substantial pain. Strep requires antibiotics to cure, and if untreated can lead to more serious complications, including scarlet fever and tonsillitis.
Influenza
Various flu strains can cause a sore throat as well.
Mononucleosis
A severe sore throat often occurs with mono.
Post nasal drip
Sinus drainage from a cold or allergies can also irritate the throat.
There are many other causes of a sore throat, and it is generally recommended that you see a doctor if your sore throat lasts for more than a few days as that could be a sign of a more serious condition.