Pneumonia: This is the most likely diagnosis given the symptoms of pain in one area of the lung, dry cough, and shortness of breath. Pneumonia is an infection of the lungs that can cause these symptoms, especially if the infection is localized to one lobe, such as the left lower lobe.

Chronic Obstructive Pulmonary Disease (COPD) Exacerbation: If the patient has a history of COPD, an exacerbation could cause these symptoms, especially if there's an increase in cough and shortness of breath.
Pulmonary Embolism (PE): While not as common as pneumonia, a PE could cause localized pain, cough, and shortness of breath, especially if the embolism is located in a segmental or larger artery supplying the left lower lobe.
Asthma: Severe asthma or an asthma exacerbation could cause cough and shortness of breath, and if the inflammation is more pronounced in one area, it could cause localized pain.
Bronchitis: Either acute or chronic bronchitis could cause these symptoms, especially if the inflammation is localized to the left lower lobe.

Lung Cancer: Although less likely, lung cancer could cause these symptoms, especially if the tumor is located in the left lower lobe. It's crucial not to miss this diagnosis due to its significant implications for treatment and prognosis.
Tuberculosis (TB): TB can cause localized lung symptoms, including pain, cough, and shortness of breath. Given its potential for serious consequences and transmission to others, it's a diagnosis that should not be missed.
Pneumothorax: A spontaneous pneumothorax could cause sudden onset of sharp pain and shortness of breath. Although it might not typically cause a dry cough, it's a condition that requires immediate attention.

Pulmonary Vasculitis: Conditions like Wegener's granulomatosis or other forms of vasculitis could cause lung symptoms, including pain, cough, and shortness of breath, but these are less common.
Eosinophilic Pneumonia: This rare condition can cause lung inflammation and symptoms similar to those described, often in response to certain medications or environmental exposures.
Lymphangitic Carcinomatosis: This condition, characterized by the spread of cancer to the lymphatic vessels of the lungs, can cause symptoms similar to those described, although it is relatively rare.