Hello and thank you for your question.
The pain could be related to remaining infection in the tooth you have had done, or the tooth next to it was the one needing the root canal
. The level of pain you are experiencing means you have a dying nerve
and are suffering from irreversible pulpitis
. Best thing to do is to go to an endodontist and have a pulp vitality test performed on all of your teeth in that area to determine which tooth is the source of pain.