What Causes Sudden Onset Of Pain In Shoulder After Shoulder Surgery?

I am four months removed from shoulder surgery to remove bone spurs, clean up a frayed labrum, and shaving of the clavicle. Post op was fine, and I was out of the sling the same day. I did do therapy and about 3 weeks ago, the pain started coming back. My should locks up and is extremely painful. There was no rotator tear at the time, but I have had that before on my other shoulder, and these symptoms are the same. I went back to the doctor and he gave me a steroid shot to see if it would help. I had this procedure done to prevent the bone spurs from tearing the rotator . What could this be?