Viral Upper Respiratory Tract Infection (URTI): This is the most common cause of the symptoms described, such as sore throat, runny nose, headache, cough, and congestion, especially given the duration of 4 days. Viral URTIs are highly prevalent and typically self-limiting.

Influenza: Given the combination of symptoms like headache, cough, and congestion, influenza should be considered, especially during flu season. The presence of a sore throat and runny nose also aligns with influenza, although these symptoms can be less prominent than in viral URTIs.
Allergic Rhinitis: If the patient is exposed to allergens, allergic rhinitis could explain the runny nose, congestion, and possibly the sore throat if there's associated postnasal drip. However, headache and cough might be less typical or less severe.
Sinusitis: This could be a consideration if the symptoms persist or worsen over time, indicating a possible bacterial superinfection of the sinuses. However, the duration of 4 days might be early for a diagnosis of bacterial sinusitis without other specific signs like facial pain or purulent nasal discharge.

Streptococcal Pharyngitis: Although less common than viral causes, streptococcal pharyngitis (strep throat) is a critical diagnosis not to miss due to the potential for complications like rheumatic fever if left untreated. The presence of a sore throat is a key symptom, but the absence of a cough and the presence of other symptoms like runny nose might make this less likely.
Pertussis (Whooping Cough): Especially in adults or individuals not up to date with their vaccinations, pertussis can present with a persistent cough and might be accompanied by other upper respiratory symptoms. It's crucial to consider this diagnosis due to its contagiousness and potential severity in unvaccinated individuals.
COVID-19: Given the current pandemic, COVID-19 should be considered in the differential diagnosis for any respiratory symptoms, including sore throat, runny nose, headache, cough, and congestion, especially if the patient has been exposed or is in a high-risk area.

Mononucleosis: Caused by Epstein-Barr virus, this condition can present with sore throat and might be accompanied by other symptoms like headache and fatigue. However, it typically includes lymphadenopathy and fever, which are not mentioned.
Lemierre's Syndrome: A rare condition characterized by a sore throat followed by neck pain and fever due to a bacterial infection, typically Fusobacterium necrophorum. It's an unlikely diagnosis without specific signs like neck swelling or sepsis symptoms.
Tuberculosis: Although extremely rare as a cause of acute upper respiratory symptoms, tuberculosis (TB) can present in many ways, including with cough and systemic symptoms like headache. However, TB would typically have a more chronic course and might include other symptoms like weight loss, night sweats, or exposure history.