Musculoskeletal Chest Pain: This is often the most common cause of chest pain in adolescents, especially given the acute onset and description of the pain as "crushing" without any specific radiation or associated symptoms like shortness of breath. The normal ECG and chest X-ray (CXR) support this diagnosis, as musculoskeletal pain would not typically alter these tests.

Costochondritis: This condition, characterized by inflammation of the cartilage that connects the ribs to the breastbone, can cause sharp pains in the chest. It's common in adolescents and can be exacerbated by movement or deep breathing.
Gastroesophageal Reflux Disease (GERD): GERD can cause chest pain that may be described as burning or squeezing, and it can be exacerbated by eating or lying down. The absence of shortness of breath and normal diagnostic tests does not rule out GERD.
Anxiety or Panic Attack: Given the patient's history of migraines, which can be stress-related, and the absence of other symptoms or abnormal test results, anxiety or a panic attack could be considered, especially if the chest pain is associated with other symptoms like palpitations or fear of dying.

Pulmonary Embolism (PE): Although less common in adolescents, PE is a life-threatening condition that requires immediate attention. The absence of shortness of breath (SOB) does not rule out PE, as some patients may not exhibit typical symptoms.
Myocardial Infarction (MI): While rare in teenagers, MI can occur, especially with underlying conditions like hypercholesterolemia or drug use. A normal ECG does not completely rule out MI, especially if the pain is intermittent.
Aortic Dissection: This is a rare but life-threatening condition where there is a tear in the aorta's inner layer. It can present with severe, tearing chest pain and is more common in individuals with certain genetic conditions affecting the aorta.

Pneumothorax: A collapsed lung can cause sudden chest pain and shortness of breath, though the latter is denied in this case. A normal CXR makes this less likely but does not rule it out entirely, especially if the pneumothorax is small.
Pericarditis: Inflammation of the pericardium, the sac surrounding the heart, can cause chest pain that may improve with sitting up and leaning forward. It's less common in healthy adolescents without a clear precipitating factor.
Spontaneous Coronary Artery Dissection (SCAD): A rare cause of chest pain due to a tear in the coronary artery, more common in young women, especially those with fibromuscular dysplasia or during the postpartum period.