What can cause left side of my jaw to lock to where I can't open mouth completely wide. I have to shift jaw to right to "unlock" it w/ a hard, loud pop?

TMJ. It sounds like you might have tempero-mandibular joint syndrome (tmj), an inflammatory and degenerative condition affecting the joint between the lower jaw and cheek bone. You should get this checked out to see what treatments are available to you. There are some dos who use omm to treat tmj. Definitely worth checking out if one is in your area.