I had root canal 3 months ago. my dentist did not prescribe antibiotics before or after the root canal. everything was good for about a month then suddenly i could not chew on the root canal tooth. the dentist and prescribed antibiotics still pain?

Tooth needs to be re-evaluated. What you have described is not uncommon. Root canal therapy is finicky, and sometimes difficult to treat effectively. There may even be a fracture in the tooth. See a specialist if necessary.

Sounds as if your root canal treatment has been, unfortunately, less than successful. Retreatmentby a root canal specialist, an Endodontist, may prove to be helpful. Return to your treating Dentist for evaluation.