This is a very common problem that patients have. The most common reason is a high bite. If a patient comes to my office with a recently filled tooth and the tooth is hurting, the first thing I do is check the bite with articulating paper. If the patient has any discomfort when biting in any excursion, I relieve the bite. Often this is all that is necessary to make the tooth comfortable.
Sometimes relieving the bite is not all that is needed. The bite can be comfortable, but a tooth can ache, or be sensitive to hot or cold. If I place a filling adjust the bite and it remains sensitive for over a month . I would consider removing the filling and examining the tooth for possible causes(
Cracks, voids, or a tiny pulpal exposure. Afterwards I place a sedative filling in the tooth and see how it responds.
If the filling was a large one, where the tooth structure was overly compromised, I recommend crowning tooth. If on the other hand the filling was small and the tooth returns to normal after having the sedative filling placed I may refill the tooth with a new filling.
Some sensitive teeth do end up requiring
root canal treatments to become comfortable, but I usually try making the tooth comfortable in these other ways, before suggesting root canal therapy.
If you have recently had a filling place and it is still sensitive, it is good idea to contact your dentist and make him aware of your situation. He(or She) is in the best position to help with your problem.