I have a different answer for you.
First, we know nothing about you. Your age makes a difference. So does your medical history, as does your gender. Such information would be helpful. In addition, how long has this been going on, what other symptoms do you have, any exam or tests, etc.
In order of likelihood, the possibilities are as follows:
Disc problems in the spine.
Gallbladder problems [pain under the right shoulder blade]
Pancreatic pain, stomach pain [occasionally under the left shoulder blade].
Pulmonary embolus, or pneumonia, or a collapsed lung [not likely]./
A problem with the great vessels in the chest [not likely].
A heart problem. I will now comment more on this:
Depending on different factors, and exam findings, any of these are possible.
If you are diabetic, for example, heart problems are much MORE likely, even with atypical symptoms. In fact, up to 75% of diabetics can have no symptoms or unusual symptoms for angina.
History and Physical is needed for diagnosis.
Don't take chances, see your doctor.
Not knowing you or examining you, it is impossible to say what the probabilities are here.
I am Dr. Thomas, double board certified US doctor.
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Come back if you have more questions, OR, if you have more information and want to clarify anything.