Gastroesophageal Reflux Disease (GERD): Eric's symptoms of a dry, unproductive cough, chest tightness, and minimal wheezing, especially with exertion, could be indicative of GERD. The fact that he has tried Nyquil and cough drops without relief and has no other systemic symptoms such as fever or body aches further supports this diagnosis. GERD can cause chronic cough and chest discomfort due to the reflux of stomach acid into the esophagus.

Asthma: Although Eric mentions minimal wheezing, asthma could still be a consideration, especially given the exertional shortness of breath (SOB) and the random nature of his coughing attacks. Asthma can present with a variety of symptoms, including cough, wheezing, and shortness of breath, which can be triggered by exertion.
Chronic Obstructive Pulmonary Disease (COPD): While less likely without a smoking history, COPD could be considered, especially if Eric has had significant exposure to secondhand smoke or other lung irritants. COPD can cause chronic cough, shortness of breath, and wheezing.
Allergic Rhinitis: Despite Eric denying seasonal allergies, an allergic component could still contribute to his symptoms, especially if he has non-seasonal allergies or sensitivities. Allergic rhinitis can cause postnasal drip, leading to a chronic cough.

Pulmonary Embolism (PE): Although the WELLS criteria indicate low suspicion for PE, it is crucial not to miss this potentially life-threatening condition. Any chest pain or shortness of breath, especially if sudden in onset, warrants careful consideration of PE, regardless of the initial risk assessment.
Cardiac Ischemia: Eric's chest tightness, even if constant and not clearly related to exertion, should prompt consideration of cardiac ischemia. This is especially important in assessing for myocardial infarction or angina, which can present atypically, especially in younger individuals or those without classic risk factors.
Pneumonia: Despite the lack of fever, body aches, or chills, pneumonia should be considered, particularly if the chest X-ray shows any abnormalities. Atypical presentations of pneumonia can occur, especially in older adults or those with compromised immune systems.

Sarcoidosis: This autoimmune disease can cause a variety of pulmonary symptoms, including cough, shortness of breath, and chest discomfort. While less common, sarcoidosis should be considered if other diagnoses are ruled out and if there are other systemic symptoms or findings suggestive of the disease.
Interstitial Lung Disease: A broad category of diseases affecting the lung interstitium, these conditions can cause chronic cough, shortness of breath, and chest tightness. They are less common and often require specific diagnostic testing, including high-resolution CT scans and sometimes lung biopsy.