Maybe not what you want to hear—I'd go see the endodontist. I had a deep filling a few months ago, but the dentist cautioned me ahead of time that while he thought the filling would work, there was a possibility it wouldn't, in which case I'd go directly to a dental surgeon for root canal. So it may have been a case of poor communication/manner on the dentist's part.

My filling tooth is also sensitive to heat & cold. Dentist had me come in for a look, poked, prodded & thumped around (no pain), and said it happens sometimes—three alternatives:

1. Live with it.
2. Get/use something like Sensodyne toothpaste
3. Get a dental sensitivity coating on the tooth (~$75)

So far, I'm using the toothpaste & living with it.

Doc