Thanks for asking the query,
After a successful root canal treatment
the tooth is completely devitalised, and sealed so there are no chances of pain.
Pain can be due to incompletely done procedure, any accidently left unexplored canal, re-infection, food lodgement between the tooth and cap, if the tooth is capped.
I would suggest you to visit a Dentist
and take x-ray of the tooth to look for any remnants of pulp tissue. You have to undergo re-RCT with the tooth.
Go for symptomatic treatment of complete mouth scaling and polishing.
Take complete course of antibiotics and analgesic
given by the Dentist.
Take lukewarm saline gargles and antiseptic mouthwash gargles.
Hope this helps out.