Musculoskeletal strain: Given the age and the distribution of pain (mid back to shoulder, arms, neck, and both shoulders), musculoskeletal strain is a common and likely cause. This could be due to poor posture, overuse, or acute injury.

Herniated disc: Could cause radiating pain from the back to the shoulders and arms due to nerve compression.
Thoracic outlet syndrome: Involves compression, injury, or irritation of the nerves and/or blood vessels (arteries and veins) in the thoracic outlet area, which could lead to pain in the shoulders and arms.
Fibromyalgia: Characterized by widespread musculoskeletal pain accompanied by fatigue, sleep, memory, and mood issues, which could explain the diffuse pain pattern.
Stress and tension: Can lead to muscle tension, causing pain in the back, shoulders, and neck.

Aortic dissection: Although rare in young individuals without predisposing factors, it's a medical emergency that presents with severe, tearing chest or back pain and could radiate to the shoulders.
Spinal cord compression: Could be due to trauma, infection, or tumor, presenting with back pain and neurological deficits.
Pulmonary embolism: Can cause sudden onset of back pain if the embolism involves the pulmonary arteries, especially if it causes a pulmonary infarction.
Infectious diseases (e.g., osteomyelitis, discitis): Infections of the bone or disc that could present with back pain and systemic symptoms like fever.

Multiple myeloma: A plasma cell malignancy that can cause bone pain, including back pain, due to lytic lesions.
Ehlers-Danlos syndrome: A group of disorders that affect connective tissues supporting the skin, bones, blood vessels, and many other organs and tissues, which could lead to musculoskeletal pain.
Scheuermann's disease: A condition that affects the thoracic or thoracolumbar spine, leading to kyphosis and back pain.
Ankylosing spondylitis: A form of arthritis that primarily affects the spine, although it can also affect other joints, leading to chronic back pain and stiffness.