Postnasal Drip (or Upper Airway Secretion): This condition often causes sore throat that worsens throughout the day due to the accumulation of secretions that drip down the back of the throat, irritating it. The absence of symptoms in the morning and the lack of purulent discharge support this diagnosis.

Viral Pharyngitis: Many viruses can cause a sore throat, and the symptoms can vary but often include a sore throat that may worsen over the course of the day. The absence of purulent discharge makes a bacterial cause less likely, pointing towards a viral etiology.
Allergic Rhinitis: Similar to postnasal drip, allergic reactions can cause increased secretions and irritation of the throat, leading to soreness, especially if the allergen exposure is more significant later in the day.
Dry Air or Irritants: Exposure to dry air, smoking, or other environmental irritants can cause throat irritation that worsens over the day, especially in the absence of protective mechanisms like saliva production, which decreases at night.

Strep Throat (Group A Beta-Hemolytic Streptococcus): Although less likely given the absence of purulent discharge, strep throat is a critical diagnosis not to miss due to its potential for complications like rheumatic fever. It typically presents with a sudden onset of sore throat, fever, and sometimes a headache, but the absence of cough and the presence of tonsillar exudates are more classic signs.
Epiglottitis: This is a medical emergency characterized by inflammation of the epiglottis, which can cause severe sore throat, difficulty swallowing, and shortness of breath. Although it's less common and typically presents with more severe symptoms, it's crucial not to miss due to its potential for airway obstruction.
Lymphoma or Other Malignancies: Though rare, persistent sore throat can be a symptom of lymphoma or other head and neck cancers. These conditions are more concerning in adults with risk factors or in the absence of typical viral or bacterial causes.

Gastroesophageal Reflux Disease (GERD): Stomach acid reflux can cause throat irritation and soreness, especially if symptoms worsen later in the day due to increased reflux when lying down or after eating.
Thyroiditis: Inflammation of the thyroid gland can cause throat pain and soreness, though this is less common and usually accompanied by other symptoms like thyroid tenderness or changes in thyroid function tests.
Tuberculosis: Although rare in many parts of the world, TB can cause chronic sore throat among other symptoms, and is an important consideration in individuals with risk factors or exposure history.