It appears you have torn rotator cuff repaired. Your surgeon and physiotherapist would have structured a rehabilitation programme for you considering the type of repair and size of tear. Usually I do not advise active movements of the arm for 6 weeks and then assisted active movements. I advise rest in a sling for 3 weeks. Pain is unusual if the surgery has been performed correctly.
There may ongoing infection of the suture anchor (unusual but possible), bursitis, or post op stiffness (most common cause). A physical examination and MRI arthrogram may help in clinching the diagnosis.