Possible causes of back pain between shoulder blades https://www.nhs.uk/conditions/shoulder-pain/:
Depending upon which nerve roots the virus affects, shingles can cause pain nearly anywhere in the body and may occur well before a rash is noticed. The pain may be most pronounced in the region between your shoulder blades but tends to concentrate on one side of your body.
(2) Epidural anaesthesia
People who have an epidural for labour or a C-Section sometimes experience intense interscapular pain. This pain resolves when the drip is slowed down and this pain goes away after labour.
(3) A vertical compression fracture in the thoracic region.
Compression fractures, often due to osteoporosis, may cause interscapular pain.
Scoliosis of the thoracic spine may cause pain between shoulder blades.
(5) Pulmonary Embolism
Pulmonary emboli occur when clots in the leg (deep vein thrombosis) break off in the leg and travels to the lungs. The pain is often sudden in onset, sharp and may be associated with severe shortness of breath, although sometimes people notice only mild discomfort.
(6) Acid Reflux
Gastroesophageal reflux (acid reflux) may cause referred pain to the back in the region between the shoulder blades. Other symptoms include chest pain, hoarseness and difficulty swallowing.
(7) Nerve entrapment
Nerve entrapment on rhomboid muscles can cause pain between the shoulder blades.
(8) Gallbladder disease
Referred pain from gallbladder disease often occurs as a stabbing pain between the shoulder blades and may be associated with pain on the right upper quadrant of the abdomen and nausea.
(9) Muscle strain
The most common cause of pain between the shoulder blades is a muscle strain. This can result from poor posture (especially leaning forward with prolonged sitting or standing), excess lifting and activities that involve twisting.
Example of this is trauma on the shoulder.
Arthritis in the neck or even the ribs may cause interscapular pain.
(12) Herniated or Bulging Discs
(13) Heart Attack
Lung cancer can cause referred pain between the shoulder.