The root canal treatment seems to be incomplete. Actually that white color stick which is seen in the xray should be placed till the tip of the root canal. But here it is not done till end. Also in crown portion the cement is not sealed properly. The most important part of endodontic treatment (Root canal treatment) is apical seal and the second thing is coronal seal. Here both are not proper. So there are chances for the reinfection from the coronal area by saliva, food particles etc and from the periapical area also. Also if the white color stick is not placed till end means that area is not cleaned and shaped properly.. So there will be remnants of pulp (which is to be removed in rct) for sure. These are the causes of pain. So u r suffering from recurrent infection of the root canal treated teeth

After seeing your x-ray what I think is that the root canal treatment is not done accurately because the filling material should be there till the end of the root of the tooth  Also there is a wisdom tooth present there which is tilted  I would also advise you to get a cbct xray done for that area.

Root canal treatment is not sone property. Usually when a rct is done the root ends should be completely filled up n sealed towards the end of the roots of the tooth. And its doesn’t seems to be the same in your case. Which reoccurrence of pain & infection can happen . And thats in ur case which has happened.

Root canal procedure involves cleaning &shaping of the canal, disinfection and then sealing off the canals.in the X-ray the steps seem to be incomplete which might have lead to some pathology still present in the canals that is causing the symptom(pain)