Jaw cramps/pain after wisdom tooth extraction

One week ago, I had a lower wisdom tooth removed which was stuck under the crown of the tooth next to it. The tooth it was stuck under has a deep cavity (about a mm left to the pulp) in the area that was between the two teeth. I am scheduled to fill it temporarily next week (and then permanently in a few months).

I am worried because most people I talk to say the pain from tooth extraction should go away quickly, while mine has not. I have no pain from the extraction site itself, but my jaw aches to the point where I use OTC pain meds to sleep, but can mostly get by without them at daytime now. It feels like there is a great deal of tension in my jaw, almost like I am having some sort of "cramps". If I massage my cheek and move my mouth around it can go away, but otherwise it turns into painful stiffness and my ear starts ringing. The pain has been slowly subsiding, but it just doesn't seem like it wants to go away fully. Is this normal?

As a secondary question, how are the odds for successfully fixing my caries-ridden tooth with filling or root canal treatment when the cavity is so deep? Since the extraction it has been sensitive to cold, but no pain. Even if the filling is successful, it will wear out after a few years, correct? So I will eventually have to pull it out too, rendering me with only one molar on that side? I've never had a single cavity in my life before, and now everything is a big nightmare :(

Thanks in advance for any replies. I would be most grateful.