Hi, I Have Been Having A Problem With Increasing Pain

Hi, I have been having a problem with increasing pain in the left and sometimes right area of my back, right under the shoulder blades. I had these pains when I had a knee replacement a couple of years ago and they did a CT scan and said everything was ok, but within the last few months the pains are increasingly worse and I have pain all throughout the day. Sometimes it is extremely painful when eating especially if I am in a chair that puts pressure on that part of the upper back.