Pain between the shoulder blades can be caused by several different things and sometimes the pain between the shoulder blades is caused by something more serious while other times the pain between the shoulder blades is less serious.
Sometimes the pain between the shoulder blades can be caused by muscle strain of the shoulder, injury to the shoulder, lifting things with your shoulder incorrectly, sleeping in the wrong position etc.
Other times the pain between the shoulder blades could be caused by things such as degenerative disc disease, or a herniated or bulging disc in the spine.
It could be that you're not sitting in the correct posture either especially if you have to sit at a desk for hours on end in an office.
I used to work in an office and had to sit for 8 hours per day and I was slouching and not sitting correctly in the correct posture and I started getting pain in between the shoulder blades.
I went to the doctor for it and he said that I was likely just straining my shoulder muscles and that if I were to sit up better in my chair that the pain between the shoulder blade should go away and it did.
If the pain in between your shoulder blades continue or seem to get worse you should see a doctor about it and get some X Rays and other imaging done to find out what exactly is causing the pain between your shoulder blades.