Hi:My suggestion is to go back to your dentist to recheck the bite and do a nerve test to make sure nerve is ok. Sometimes X-ray does not show nerve damage right away.Best,Dr. Maddahi
It is unlikely that decay under the crown of a root canaled tooth would cause the symptom you described. You should have the root canal result evaluated by an Endodontist to determine if all is well with the root canal procedure. Crack tooth syndrome is also a possibility.