Viral Upper Respiratory Tract Infection (URTI): This is the most common cause of the combination of symptoms like eye discharge, sore throat, and post nasal drip. Viruses such as rhinovirus, coronavirus, adenovirus, and respiratory syncytial virus are often responsible.

Allergic Rhinitis: This condition can cause eye discharge, sore throat (due to post nasal drip), and is often associated with other symptoms like sneezing, nasal congestion, and itchy eyes.
Bacterial Pharyngitis: Although less common than viral URTI, bacterial infections like streptococcal pharyngitis can cause sore throat and, if associated with a sinus infection, could lead to post nasal drip and eye discharge.
Sinusitis: Inflammation of the sinuses can cause post nasal drip, which may lead to sore throat and, in some cases, eye discharge if the sinuses are infected and the infection spreads.

Invasive Bacterial Infections (e.g., Meningitis, Orbital Cellulitis): Although rare, these conditions can present with similar initial symptoms but are much more severe and potentially life-threatening. Early recognition and treatment are crucial.
Lemierre's Syndrome: A rare but serious condition that starts with pharyngitis and can progress to septicemia and thrombophlebitis of the internal jugular vein, potentially causing severe complications.

Wegener's Granulomatosis (Granulomatosis with Polyangiitis): A rare autoimmune disorder that can cause a wide range of symptoms including sinusitis, sore throat, and eye symptoms due to granulomatous inflammation of the respiratory tract and necrotizing vasculitis.
Sarcoidosis: Another rare condition that can affect multiple parts of the body, including the lungs, skin, and eyes, potentially causing symptoms similar to those described, although it would be an unusual presentation.
Tuberculosis: Although more commonly associated with pulmonary symptoms, TB can cause a wide range of symptoms including those affecting the eyes and throat, especially in immunocompromised individuals or in areas where TB is common.