Hello
Good to see a young boy taking care of her mother, the possibility can be any of these,1) Reinfection of that tooth,,so it might need 're rct
2) any other tooth involvement
3) any fracture of the root canal treated tooth if capping not done
Next Steps
visit your nearby dentist and get it diagnosed
Health Tips
try not to eat from that side as it will further detiorate the condition, till the time take some pain killer for some relief