Welcome to HCM,
You have not mentioned your age.
If you are elderly then there is possibility of having some degenerative changes in your cervical spine
, called Cervical spondilitis.
Here there is pressure or irritation on nerves giving rise to pressure symptoms causing pain in shoulder blade area or in the arms.
You get relief while lying down position due to pressure released of nerves from cervical vertebrae
In young this problem may occur due to having extra cervical rib
Consult orthopedic surgeon and get examined.
Ok and bye.