Pain on biting down, pain all the time regardless, or pain with hot & especially cold?
This problematic tooth may have a fracture
which is not showing up on a radiograph. If the nerve
in the tooth went bad, then you may have a sinus infection.
The key to solving your problem is first to determine id the nerve in the tooth died. This can be done with a vitality test. If the nerve has died, then the tooth needs a root canal
If the nerve in the tooth is still alive, then it needs to be determined if there is a crack and how deep it is.
Since you have gone to two generalists and still have a problem, i suggest you see an endodontist (root canal specialist) who will make the determination after an exam as to the proper course of treatment.
Hope this info helps.