Thanks for writing in.
The PAIN after root canal treatment
can be due to many reasons-
1.Secondary infection of the tooth.
2.Improper technique of rct performed.
3.Perforation/ledge formation occured during rct.
4.Periapical infection beneath the root canal treated tooth.
I would suggest you to visit your dentist
and get a thorough clinical and radiological examination to find out the cause.
Treatment can be planned according to that.
IF necessary,re-rct has to be done.
and curettage of abscess has to be done if periapical abscess
The tooth has to be restored permanently unless the abscess has drained completely.
Meanwhile,take complete course of antibiotics-analgesics prescribed by your dentist.