Costochondritis: This condition, also known as Tietze's syndrome, is characterized by inflammation of the cartilage that connects the ribs to the breastbone. It is a common cause of chest pain in adolescents and can cause sharp pains that worsen with deep breathing or coughing, fitting the patient's symptoms.

Musculoskeletal strain: Given the patient's age and the nature of the pain, a musculoskeletal strain from overuse or minor trauma could be a plausible explanation. The pain worsening with inspiration could be due to the movement of the ribcage.
Intercostal muscle strain: Similar to musculoskeletal strain, intercostal muscle strain could cause pain that worsens with deep breathing or movement.

Pulmonary embolism (PE): Although less common in adolescents, PE is a life-threatening condition that requires immediate attention. The denial of shortness of breath and other typical symptoms does not rule out PE, as presentations can be atypical.
Pneumothorax: A collapsed lung can cause sharp chest pain that worsens with breathing. Even without shortness of breath, a pneumothorax needs to be considered and ruled out with imaging.
Osteomyelitis or rib fracture: Infection of the bone or a fracture could cause localized pain that worsens with movement or deep breathing. These conditions are less likely without a history of trauma but should not be missed due to their potential for serious complications.

Sickle cell crisis: If the patient has sickle cell disease, a crisis could cause severe pain, including rib pain, due to vaso-occlusion.
Tuberculosis (TB): TB can cause chest pain, among other symptoms, and is more likely in individuals with recent travel to or contact with someone from an area where TB is common.
Lymphoma: Although rare, lymphoma could cause chest pain due to mediastinal involvement. It would be an unusual presentation without other systemic symptoms, but it should be considered in a broad differential diagnosis.