Tonsillitis: It is an inflammation of the tonsils on either side of the back of throat. When one tonsil becomes infected more than the other, it can cause one-sided throat pain. Symptoms often include: 
Swollen, red tonsils, White or yellow coating on the tonsils, Painful swallowing and Fever.

Abscess: A peritonsillar abscess is a collection of pus that forms near the tonsils, typically on one side. This condition is more serious and requires medical attention. Symptoms include: 
Excruciating throat pain on one side, High fever, Redness and Swelling and Difficulty in opening mouth.

Canker Sores: Canker sores are also known as aphthous ulcers and these are small and painful sores, developing on the mucous membranes. They typically grow inside the mouth or on the gums. These ulcers may be triggered by various factors including trauma, injury, stress, toxins, allergies, or immune system disorders. Moreoever, a burning sensation may accompany the appearance of canker sores after a day or two. The sore eventually manifests as a red or gray lesion that may drain fluid. While canker sores primarily develop on mucous membranes, they can affect multiple areas, such as, throat, cheeks, lips, floor of the mouth, and soft palate.

Lymph Node Swelling: Certain infections and swelling may prod the lymph nodes on one side of the neck to swell. This swelling may result in utter pain, and it feels like it has occurred in the throat. Furthermore, this lymph node swelling is often accompanied by: 
Swollen nodes, General Malaise and Fever.

Pharyngitis: Pharyngitis, an inflammation of the pharynx, can sometimes be localized to one side. This inflammation or condition could result either from viral or bacterial infections. Symptoms may include: 
Difficulty swallowing, Sore and red, swollen throat.

Glossopharyngeal and Trigeminal Neuralgia: Glossopharyngeal and trigeminal neuralgia may result due to the compression or irritation of their respective nerves, developing intense and excruciating throat pain. These conditions can arise spontaneously or develop due to factors such as: 
Tumors, Dental work, Facial injury or trauma and Facial swelling. Furthermore, the pain from these neuralgias is typically intense and acute, or shock-like, and can last from several seconds to several minutes. 

Gastroesophageal Reflux Disease (GERD): GERD can cause stomach acid to fall back to esophagus. This falling back of stomach acid or GERD may sometimes affect only one side of the throat, leading to intense or severe pain. Other symptoms may include: 
Acidic taste in the mouth, Sudden heartburn, Sore throat, often growing worse at night or after eating. 

Dental Issues, Tooth Abscess or Infection: Infections or tooth problems, especially at the side of the mouth, may lead to throat pain. Dental issues such as tooth abscess can rapidly escalate, causing swelling and pain that radiates to other areas of the mouth including the throat. In addition to this, throat pain particularly on one side or near a problematic tooth may indicate a dental problem. Additional symptoms can include swollen lymph nodes, fever, and difficulty swallowing.

Cancer: Although less common, throat cancer can cause one-sided throat pain. Symptoms to watch for include: A lump in the neck, Persistent sore throat, Unexplained weight loss and Difficulty in swallowing.

Injury or Irritation: Physical pain in one side of the throat, such as, from swallowing a sharp object or excessive shouting, can cause localized pain. Chemical irritants like smoke or harsh fumes can also lead to one-sided soreness or throat pain.