Gastroesophageal Reflux Disease (GERD): The chest pain worsening with laying down is a classic symptom of GERD, as gravity can exacerbate reflux when in a supine position. The normal EKG and lack of other cardiac concerns also point away from cardiac causes, making GERD a plausible explanation.

Musculoskeletal Pain: Chest pain that is exacerbated by movement or position, such as laying down, can be due to musculoskeletal issues like costochondritis or muscle strain. The spreading nature of the pain could indicate involvement of multiple areas.
Pulmonary Embolism (less likely due to duration but still a consideration): Although less likely given the duration of symptoms and the lack of other concerning features like shortness of breath or significant risk factors, pulmonary embolism can sometimes present with chest pain that worsens with deep breathing or position.
Pericarditis: This condition can cause chest pain that improves with sitting up and leaning forward, but it can also worsen with laying down. However, pericarditis often has associated findings like a pericardial friction rub, and the EKG might show changes, although not always.

Aortic Dissection: Although very unlikely given the normal EKG and lack of other symptoms like severe, tearing pain or differential blood pressures in limbs, aortic dissection is a catastrophic condition that must be considered in any patient with chest pain.
Pulmonary Embolism: As mentioned, while less likely, the potential consequences of missing a pulmonary embolism make it a "do not miss" diagnosis.
Myocardial Infarction (MI) with Normal EKG: While the EKG is normal, it's crucial to remember that early in the course of an MI, the EKG can be normal. The absence of other cardiac concerns does not rule out MI entirely, especially in younger patients or those with atypical presentations.

Esophageal Spasm: This condition can cause chest pain that mimics cardiac pain but is due to abnormal esophageal contractions. It's less common and might be considered if other diagnoses are ruled out.
Pneumothorax: Spontaneous pneumothorax can cause sudden onset chest pain that worsens with deep breathing or position. It's less likely given the gradual onset and absence of respiratory symptoms, but it remains a rare consideration.
Mediastinitis: Inflammation of the mediastinum can cause chest pain, but it's often associated with other symptoms like fever or signs of infection, making it a less likely but rare consideration.