I imagine the problem is in your neck as you didn’t specify the area of pain and OPLL only occurs in the neck. According to your post, you have multiple degenerative discs in the cervical spine and ossification of the posterior longitudinal ligament- either which may be compressing the “spine”. 3 separate problems can occur with what I understand is your condition. You could develop narrowing of the spinal canal called cervical stenosis- symptoms of cord compression would not be pain but would be incoordination of the hands, imbalance with walking, pins and needles of the hands and legs and eventually- bowel and bladder habit changes.
If you developed compression of the nerve root in the neck, you would develop arm pain that would be made worse with bending the head back or to the side of pain, associated with pins and needles in the arm, possible weakness and numbness.
You could develop neck pain. This would manifest as local pain made worse with activity or impact.
Hope this helps.