Mechanical Low Back Pain: This is the most common cause of lower back pain and can be associated with cracking sounds due to the movement of joints and ligaments. Justification: The symptoms of new onset aching discomfort and constant cracking with movement are typical for mechanical issues related to the musculoskeletal system of the lower back.

Lumbar Facet Joint Syndrome: This condition involves inflammation of the facet joints in the spine, which can cause pain and cracking sounds. Justification: The constant cracking with movement suggests involvement of the facet joints.
Ligament Sprain: A sprain in the ligaments of the lower back can cause pain and instability, leading to cracking sounds. Justification: Sudden onset of symptoms after a specific incident or increased activity level could indicate a ligament sprain.
Muscle Strain: Strain in the muscles of the lower back can cause pain and stiffness, potentially accompanied by cracking sounds due to muscle spasms. Justification: Overuse or sudden contraction of the back muscles can lead to strain, fitting the symptoms described.

Cauda Equina Syndrome: A serious condition where the nerves in the spinal canal are compressed, requiring immediate medical attention. Justification: Although less likely, the presence of new onset lower back pain with any neurological symptoms (e.g., numbness, weakness, bladder/bowel dysfunction) necessitates consideration of this diagnosis due to its severe consequences if missed.
Spinal Infection (e.g., Discitis, Osteomyelitis): Infections of the spine can cause severe back pain and require prompt treatment. Justification: Fever, recent travel, or immune compromise could increase the likelihood of a spinal infection, making it crucial not to miss this diagnosis.
Spinal Fracture: A fracture in the spine can cause sudden onset of back pain and may be associated with cracking sounds. Justification: Trauma, osteoporosis, or cancer could predispose to a spinal fracture, which is a critical diagnosis not to overlook.

Spondyloarthropathies (e.g., Ankylosing Spondylitis): Chronic inflammatory diseases that can cause back pain and stiffness, potentially leading to cracking sounds due to joint involvement. Justification: These conditions are less common and typically have a more gradual onset, but they should be considered in patients with persistent symptoms and systemic signs of inflammation.
Spondylolisthesis: A condition where a vertebra slips out of place, which can cause back pain and potentially cracking sounds. Justification: This condition might be more common in certain populations (e.g., young athletes) and could explain the symptoms if other more common causes are ruled out.