Heat sensitivity after root canal and ill fitting crown.

I had a root canal done on an upper molar about 6 weeks ago and a crown put on a few weeks after that. Initially it felt fine. We've had a hard time getting the adjustment right on the crown and my upper and lower jaw have been aching because of it. It seemed to be getting better, although not completely right, when a few days ago I noticed that area became mildly sensitive to heat. What could be going on?