Musculoskeletal strain or costochondritis: This is the most likely diagnosis given the location of the pain (between the left shoulder and chest anterior), the exacerbation of pain with movement and touch, and the lack of response to initial treatments. The normal vital signs (VS) also support a non-life-threatening musculoskeletal issue.

Rib fracture or contusion: Although the patient does not mention a history of trauma, a minor injury could have been overlooked or forgotten. Pain with movement and touch is consistent with a rib injury.
Tietze's syndrome: This condition involves inflammation of the cartilages and surrounding tissues of the ribs and can cause sharp pains in the chest that worsen with movement or coughing.
Gastroesophageal reflux disease (GERD): While GERD typically presents with heartburn and regurgitation, some patients may experience chest pain, especially if the pain is referred.

Myocardial infarction (MI) or acute coronary syndrome (ACS): Although the patient's vital signs are normal and the pain is described as being between the shoulder and chest anterior, cardiac causes of chest pain must always be considered, especially in patients with risk factors for coronary artery disease. The fact that nothing is helping with the pain raises concern for a more serious condition.
Pulmonary embolism (PE): Sudden onset of chest pain, especially if it worsens with deep breathing or movement, could indicate a PE, which is a life-threatening condition.
Aortic dissection: This is a rare but critical condition where the inner layer of the aorta tears. It can cause severe, tearing chest pain that may radiate to the back or arms.

Pancoast tumor: A type of lung cancer located at the top of the lung that can cause shoulder and chest pain due to invasion of the brachial plexus or ribs.
Sickle cell crisis: In patients with sickle cell disease, a crisis can cause severe pain episodes, including chest pain, due to vaso-occlusion.
Herpes zoster (shingles): Before the rash appears, patients may experience pain in the distribution of the affected nerve, which could be mistaken for musculoskeletal pain.