Thanks for asking the query,
After sucessful root canal treatment
the canals are completely devitalised, disinfected and sealed to the apex so there are no chances of pain.
Pain after the treatment indicates incompeltely done procedure, any left over pulp tissue or re-infection.
I would suggest you to visit the concerned Dentist
and get the checkup done take an x-ray done, depending upon which re-RCT can be performed if needed.
Take complete course of antibiotics and analgesics.
Maintain a good oral hygiene
, use antiseptic mouthwash rinses.
Hope this helps out.