A month after root canal and crown my pre-molar still hurts. the dentist checked it twice and said the canal looks perfect. is this just sensitive?

CBCT: It might be a bite problem, a micro fracture in the tooth or root, an unfilled accessory canal or some other problem that cannot be seen either on clinical exam or with 2-dementional x-ray. You might want to have a consult with an endodontist who can take a cbct (cone beam ct 3d scan) which often shows previously undetectable problems. Or you can wait it out awhile longer.

Maybe: In many cases, it takes a while for the tooth to feel just right. The radiograph may look perfect, but there might be something amiss. Although a month has passed, give it a bit more time to heal.. The alternative is to take everything apart, and you don't want to go that route unless absolutely necessary.

Time: If the root canal looks good, sometimes adjusting the bite a little will help. Sometimes it just takes some time to completely settle down.