Ever since my acdf at c5 to c8 two years ago i have been having severe pain between my shoulder blades in thoracic spine. feels unstable ?

Be seen: Certainly would want to be seen and thoroughly evaluated. Sometimes it can be a problem at the surgical site such as a nonunion, sometimes can be an adjacent level, or sometimes it can be another problem entirely. A myelogram with post myeligram cr scan of thoracic and cervical spine may be of benefit. If you are not satisfied with answer you get, consider second opinion.