What is the differential diagnosis for a 24-year-old female presenting with shortness of breath (SOB) and left-sided chest pain for 4 days, with a normal electrocardiogram (ECG)?

Musculoskeletal chest pain: This is often the most common cause of chest pain in young adults, especially when the ECG is normal. The pain is typically sharp, worsens with movement, and can be reproduced by palpation.

Pulmonary embolism (less likely due to age but possible): Although less common in young adults without risk factors, it's still a consideration, especially if there's a history of recent immobilization, surgery, or family history of clotting disorders.
Pneumonia: Could present with chest pain and shortness of breath, especially if the pain is pleuritic (sharp pain that worsens with deep breathing).
Asthma or COPD exacerbation: These conditions can cause chest pain and shortness of breath, particularly if the patient has a history of respiratory disease.
Gastroesophageal reflux disease (GERD): Can cause chest pain that may be mistaken for cardiac or pulmonary issues, especially if it radiates to the chest.

Acute coronary syndrome (ACS): Although rare in young females, it's crucial not to miss this diagnosis. Risk factors such as familial hypercholesterolemia, drug use (e.g., cocaine), or other cardiovascular diseases increase the likelihood.
Aortic dissection: Extremely rare in this age group without predisposing conditions (e.g., Marfan syndrome, Ehlers-Danlos syndrome), but it's a medical emergency.
Pulmonary hypertension: Could present with shortness of breath and chest pain, and is critical to diagnose early due to its poor prognosis if untreated.

Pneumothorax: More common in tall, thin males, but can occur in anyone, especially with a history of lung disease.
Pericarditis: Inflammation of the pericardium, which can cause chest pain that may improve with sitting up and leaning forward.
Mitral valve prolapse: Can cause chest pain, although it's more commonly associated with palpitations and murmurs.