What is the diagnosis for a 68-year-old male with a history of Chronic Kidney Disease (CKD), Hypertension (HTN), Hyperlipidemia (HLD) and Prediabetes, who also reports seasonal Allergic Rhinitis, presenting with a 3-day history of nasal congestion, postnasal drainage, and a productive cough with phlegm, but no chest pain, shortness of breath, or fever?

Acute Viral Rhinosinusitis (Common Cold): The patient's symptoms of nasal congestion, postnasal drainage, and cough with phlegm are classic for a viral upper respiratory infection, which is very common and often triggered by seasonal allergies.

Allergic Rhinitis: Given the patient's history of seasonal allergies, his current symptoms could be exacerbated by or primarily due to an allergic reaction, especially if the symptoms are seasonal and correlate with specific allergen exposure.
Acute Bronchitis: This condition, often caused by a viral infection, could explain the cough and phlegm production. It's more likely in someone with a history of smoking or other respiratory irritants, but can occur in anyone.
Chronic Rhinosinusitis: If the patient has a long-standing history of similar symptoms, chronic rhinosinusitis could be considered, especially if symptoms persist beyond the typical duration of a viral infection.

Pneumonia: Although the patient denies fever, chest pain, or shortness of breath, pneumonia can sometimes present atypically, especially in older adults. It's crucial to consider this diagnosis due to its potential severity and the need for prompt antibiotic treatment.
Chronic Obstructive Pulmonary Disease (COPD) Exacerbation: If the patient has undiagnosed COPD, an exacerbation could present with increased cough and phlegm production. This is particularly important if there's a history of smoking or exposure to lung irritants.
Heart Failure: In patients with a history of hypertension and hyperlipidemia, heart failure is a possibility, especially if there are signs of fluid overload. However, the absence of shortness of breath or chest pain makes this less likely.

Invasive Fungal Sinusitis: This is a rare but serious condition, more likely in immunocompromised patients or those with poorly controlled diabetes. The patient's prediabetes and chronic kidney disease might slightly increase his risk, but this remains a rare consideration.
Wegener's Granulomatosis (Granulomatosis with Polyangiitis): A rare autoimmune disorder that can cause respiratory symptoms among other systemic issues. It would be an unusual diagnosis without other supporting symptoms like weight loss, fever, or specific findings on physical examination.