What should I do about severe swelling after root canal?

Is it the tooth that is hurting or your jaw? Usually with a root canal, and especially in a back molar, you have to hold your mouth open very wide for extended periods of time. That is usually what causes pain and soreness the next day. The tooth no longer has any nerve in it so that should not be hurting. The advil is a good choice, but if you continue to have pain I would at least call the endo's office and ask about it. ~~Good luck to you