It's not winging it it?
sticking out or looking crooked compared to the other side?

If not that then we need to figure out if it is the blade itself or any of the muscles/nerves in that area.
I doubt that it is the actual bony part of the blade, has to be something around or under it.

If you can describe the location & how the pain feels we might be able to pin it down.
But if it is really bad a pro PT evaluation might be best if you can get the dr to rx that. I think it would be good to let them know this is happening and they should check it out just in case ...
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I do know that the rhomboids are located under the edge of the shoulder blade. They can get over stretched very easily and will feel like a knife in the back right under the scapula when that happens.

Mine will get over stretched when I allow my shoulders to roll forward for long amounts of time, or if i am holding and reading a book for long times.
For me it is a deep ,burning, achy pain.
I can get rid of it by keeping my shoulders back and laying on the ball or foam roller so gravity helps to let the shoulders relax and drop back to normal.