Few days.... There generally is pain after the local anesthetic wears off; the dentist should explain and warn about that depending how invasive the procedure is, whether he had to clear out infection, or abscess at the root. He should also give you a script for pain medication appropriate to the procedure, and appropriate to his knowledge of your pain threshold and ability to handle pain. Call, get advice.
Depends. Usually a few days. Often your dentist will prescribed pain medication to help you.