Pain in my jaw area after a root canal. How long will it last?

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.
Days-weeks, but. Days to weeks. However, not all root canals cure the problem. If your symptoms persist, go back to dentist. If the dentist was not an endodontist (root canal) specialist. Consider seeing an endodontist for a second opinion with persistent symptoms.
1-2 weeks. Depending on the severity of the infection, root canal pain should diminish within 1-2 weeks. There are occasions when the infection may require additional antibiotic therapy and may delay return to normal for up to 6-8 weeks.