Hello,
Many different conditions may be responsible for this type of symptom.
Strained muscles and sprained ligaments are among the most common causes of left upper back pain. This usually occurs when excessive pressure, often from exercising too much, causes the tissue to stretch too much or excessively, causing them to become damaged or torn. Pulled muscular tissue and pinched nerves are other possibilities. Take some over the counter anti-inflammatory painkiller like ibuprofen. Hot compressions, and topical muscle relaxants are also helpful.
Fibromyalgia, a soft tissue form of rheumatism may also cause burning and aching in the shoulder blade area.
More serious causes of upper back pain include osteoporosis(a disease in which the bones become porous and fragile—so fragile, that a vertebrae can shatter, just from the spine's own weight.), a ruptured spinal disk(rare),injury, heart disease and GERD(both of these cause referred pain)
If the symptoms persist after pain killers and muscle relaxants also,then pls consult an orthopedician to rule out other possibilities.
Take care and pls do keep us posted on how you are doing.
I can't tell you what it is, but I can tell you that I am having similar issues. Especially the part about it hurting more if you lean to the opposite side. I also get some relief from sleeping on my side, but have more pain from sleeping on the opposite side of the pain.
Does it feel like the pain is underneath your scapular bone? Is there any grinding or popping when you move your arm? Does it hurt when you take in a really deep breath?
It could be a pinched nerve in your spine, could be a scapula problem... are you going to see a doctor?