Mechanical Low Back Pain: This is the most common cause of back pain in adults, often exacerbated by prolonged sitting, lifting, or bending. The patient's symptoms of back pain worsening with long hours of sitting support this diagnosis.

Musculoskeletal Strain: Given the patient's age and the nature of the pain, musculoskeletal strain from overuse or poor posture is a plausible cause.
Herniated Disc: Although less common, a herniated disc could cause back pain that worsens with sitting due to increased pressure on the disc.
Degenerative Disc Disease: Early onset of degenerative changes in the spine could lead to back pain, especially with prolonged sitting or standing.

Spinal Infection (e.g., Osteomyelitis, Discitis): Although rare, spinal infections can present with back pain and must be considered, especially if there's a fever, recent travel, or immunocompromised state.
Cauda Equina Syndrome: A medical emergency characterized by low back pain, sciatica, and neurological symptoms such as bladder or bowel dysfunction. Early recognition is crucial.
Spinal Tumor: Tumors in the spine can cause back pain, and while rare, missing this diagnosis could have severe consequences.

Spondyloarthritis (e.g., Ankylosing Spondylitis): Inflammatory conditions of the spine that can cause back pain, stiffness, and limited mobility. These conditions are less common and typically have additional symptoms.
Osteoporotic Compression Fracture: Although more common in older populations or those with osteoporosis, a compression fracture could occur in a younger individual, especially with significant trauma or osteoporosis risk factors.
Paget's Disease of Bone: A chronic condition that can result in enlarged and misshapen bones, leading to back pain among other symptoms. It is rare and typically affects older adults.