It could be your heart. When I had my heart attack that was one of the pains I had.
There are many reasons for a sharp pain. These may include, a sudden jerk, some tearing of tissue, due to some other diseases, and sometimes the problem with the heart also causes the pain behind shoulder blade.
Pain in the shoulder blade can also be a tubal pregnancy if accompanied by pain in the side.
It could possibly be a sign of nerve disturbances or just a normal sign of aging. If not, maybe it's a sign of stress. If the pains continue, it could be the Basia in your shoulder that's inflamed. Go see the doctor and start exercising that muscle more AFTER you've taken medications or keep a warm ice pack on it for two weeks one hour per night. I doubt it could be a disorder but just check with your doctor.
You may have a pinched nerve depending on what you sit on, or the tasks you perform throughout the day. I found that acupunture is a great help with this or you can see your doctor about cortizone shot
I have the same problem, but when I went in to the ER (it was 1 am when the pain was so bad I couldnt even breath) they ran blood tests and had me hooked up to a machine to read my heart. The main doc told me my heart was acting very normal, even for my wieght (!!!!!)...they sent me home and after about 3 days the pain was gone. TWO weeks after that, it shot through my shoulder and neck again, this time I was about to cry. I suffered through the night and then left on vacation the next day. During my 2 week vacation the pain came and went, but not too bad like the second and first times. Now that I am back three days ago, the pain is minimal but always there in my shoulder. I am going to go see a my actual doctor and will get back with you on here if he says anything useful...you know how it can go..pay to be told what you know LOL.