See an endodontist( root canal specialist) in your area, who specializes in performing quality root canal treatment in predictable and scientific way..

Get a diagnostic x-ray done to confirm the condition of tooth, if all well get a cap done it will be alright

Simple you have to go for x Ray First than also need to clinically check,  hope your tooth not get fractured. After diagnose than we can decide what treatment need to be done.

Reinfection of root canal is quite common due to uncertain pattern of pulp cavity and designing of canals in a tooth. Anatomy of a tooth plays vital role in the success of root canal. I would suggest you to go for re treatment. If re-treatment also fails in few months than better to get it extracted and replace it with a false tooth.

If the root canal treated tooth is paining you should visit your dentist & get an xray done.  post the xray here & then only we will be able to guide you.  But most likely you will have to get retreatment done for that tooth & this time around please get a cap made. Hope this helps.

Not placing a crown could have led to micromanage and reinfection. You need to get retreatment done

Sounds like a reinfection as cap has not been placed. Tooth filling may have chipped off a bit over the period of time which led to bacterial sipage and reinfection. Visit a dentist and get it treated properly.

Hello dear practo user, Its difficult to comment without an xray of the tooth .. so if possible, post a recent xray of the tooth .. anyways looking at what u have said, i feel there might be a reinfection that has taken place.. and it might be because of either micro leakage or improper root canal treatment or any other reason.. so re treatment is the best option for you.. and this time dont avoid placing a crown over it ..a crown really helps in many ways and can extend the life of your tooth .. all the best.