The filling on my lower back molar came off and I had a root canal done on this tooth two weeks ago. Since then, the tooth has always been sore. It's fine in the morning but as soon as I eat or drink anything, it would start aching and stays like that until I go to sleep at night. I avoided eating on that side of my mouth. I have been to the dentist twice; he took x- rays, checked my bite and said everything looked perfect. During my last visit, he gave me antibiotics for 5-days because he thought there might still be some infection in the bone. I will go back to him when I finish the antibiotics. How long should a root canalled tooth hurts? My mom said a should only hurt for 3-5 days or so based from her own experience. I've got a feeling that the canal has not worked. Any ideas? I would be grateful for any information.