Costochondritis: This condition, also known as Tietze's syndrome, involves inflammation of the cartilage that connects the ribs to the breastbone. It is a common cause of chest pain that worsens with deep breathing or movement, making it the most likely diagnosis given the patient's symptoms.

Musculoskeletal strain: Strain or injury to the muscles or ligaments in the chest wall can cause pain that is exacerbated by deep breathing or movement.
Precordial catch syndrome: A benign condition characterized by sharp, stabbing pain in the chest that can be triggered by deep breathing or movement.
Breast pathology: Conditions such as breast cysts, mastitis, or breast cancer could cause localized pain, although these would typically be accompanied by other symptoms like a palpable mass or nipple discharge.

Myocardial infarction (MI) or acute coronary syndrome: Although less likely given the location and nature of the pain, cardiac causes of chest pain must always be considered due to their potential severity and the need for urgent intervention.
Pulmonary embolism (PE): A blood clot in the lungs can cause chest pain that worsens with deep breathing (pleuritic chest pain), and it is crucial to rule out this life-threatening condition.
Pneumothorax: Air in the pleural space can cause sharp chest pain that worsens with breathing, and it requires immediate medical attention.

Sickle cell crisis: In patients with sickle cell disease, a crisis can cause chest pain due to vaso-occlusion in the chest wall or lungs.
Tietze's syndrome variant involving the xiphoid process: A rare condition where the inflammation involves the cartilage of the xiphoid process, causing lower chest pain.
Slipping rib syndrome: A rare condition where the ribs slip out of place, causing chest pain that can be exacerbated by movement or deep breathing.