It sounds like the bite or occlusion is off from what you are describing. This happens but is not normal and should be adjusted, you should not have any pain.
i would suspect that either the bite is "high" and needs to be adjusted, or perhaps taken out of occlusion entirely (although just ever so slightly) or your tooth may have a fracture/crack. cracks occur in root canal teeth much more frequently than vital teeth because they become brittle due to removing the nerve and hence the blood supply from the tooth. The tooth may have been cracked for a while (perhaps even before the root canal was done) and only now are you feeling it because you are able to put pressure on it since your crown was designed to come into contact with the opposing tooth. Many times, cracks are not visible on x-rays, and manifest themselves only with pain upon biting or pressure. later on, an abcess may appear on a film--sometimes months and months later......