Hi,
Welcome to the ehealthforum. Your concern is regarding the pain between the shoulder blades.
From the symptoms it can be a muscular pain or pain due to spinal problems. Secondly,it can be due to spasticity of the trapezius and underlying smaller muscles. The spasticity of the muscles can be brought on by overuse or trauma to the muscle.
I feel that physical examination by an orthopedician is required to confirm a diagnosis.You may also need an x-ray or a MRI spine to confirm the diagnosis. Till then,give rest to your shoulder.Apply some cold packs and some analgesic(pain reliever)gel or cream.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care.