Why is my cheek and jaw swollen with my toothache? I think I have a cavity in one of my back molars. It's been hurting for a few weeks but now my cheek is all swollen like I got punched in the face. What is causing that?

See dentist ASAP. You may have an infection that is spreading through your fascial space and these can get dangerous and need hospitalization if not taken seriously. You will likely need the abscess to be drained and then either the tooth needs to be extracted or root canal treatment may be needed to save the tooth, if it is restorable.
You . You probably have an abcess. See professional care as soon as possible.
Go to dentist asap. Swelling in you cheek is a sigh of an infection and needs immediate attention. This can be serious. You do not want to mess around with an infection. You need treatment as soon as you can get to your dentist.