Why am I having throbbing pain years after root canal/new crown in place?

A few years back by a previous dentist I got a root canal done on a molar. A year ago, from my new dentist, a permanent crown was put onEver since, I have been experiencing sensitivity in the area, and sometimes pain but never lasting long. Out of nowhere I have been dealing with some pretty intensive pain where it throbs. Immedientially went to the dentist but advised me to go to a specialist. He gave me antibiotics and some meds but I'm not feeling much relief yet. What should I do!