Thanks for your query, I have gone through your query. The pain can be because of the remnant infection in the root tip. Nothing to be panic, take a course of antibiotics like amoxicillin and metronidazole for 5 days and analgesics like diclofenac. Later you can get the tooth treated with root canal treatment. Mean while get the root canal irrigated or cleaned with saline or hydrogen peroxide. It may take 5 days for the pain to come down. I hope my answer will help you, take care.