pain 4 days after root canal

I recently had my first root canal on a tooth that was crowned a few years ago. (They put the permanent crown back on after the procedure.) Unfortunately I still feel that same nerve pain when I bite down and I cannot tolerate cold or even room temp liquids on that side of my mouth. The dentist has told me to use Sensodyne and wait a few more days. It doesn't seem to be working. I also have a large silver filling in the tooth in front of where the root canal was done. I'm wondering if it's possible that they missed something on the x-rays they took after the procedure? Maybe the root canal isn't complete and the tooth next to it is also in need of a root canal? I'm also 14 weeks pregnant which makes all of this difficult to try and deal with. Anyone have pain like this afterwards but it eventually went away??