Crown Issues

I had an upper back tooth prepped for a crown back in March, and received a temp crown while waiting for the permanent.  A couple weeks later the temp fell off and extreme sensitivity followed, even with the temp cemented back on by the dentist.  Shortly after, the permanent was delivered and adjusted twice for the bite.
Its not about 2 months later and I have been extremely sensitive to cold, sweets, and air.  In addition, I still can't chew anything but soft food on that side without significant pain.
Last week I went to the dentist again, and it seemed my bite needed to be adjusted again, however he felt that even if he adjusted it it would move back again so tried to think of another cure.  His idea was a night guard, however I am apprehensive to spend $700 on a guess when I am just wondering if its something as simple as a bad crown with poor margins that is causing the sensitivity and tenderness?  Or possibly it just needs to be adjusted one more time now that the tooth has had more time to calm down?  My concern is that the dentist wasn't really sure on the next step should be and maybe I should look for a second opinion?