Why do teeth ache after fillings?
See, since it was a simple drilling followed by restoration or filling, that means the infection was superficial, not involving the pulp where the nerves and blood vessels are situated.
Ok, so now to remove the superficial infection the dentist might have used an airotor. It's an instrument which rotates at high speed, has a hole for water spray to cool the fictional heat generated while it removes the caries or the infection from the tooth.High speed handpieces
Now as you may be knowing the crown portion of tooth has three layers- enamel, dentin and pulp. Only the pulp portion is innervated.
Now when the instrument is drilled into the tooth the infected enamel and superficial infected dentin must have been removed.
The dentin has numerous tubules known as dentinal tubules. These contain a fluid called dentinal fluid. Whenever there is any stimulus which has not yet reached the pulp, but may have reached the dentin, eg of stimulus in the form of pressure, temperature change, sweet food, sour food etc, cause the fluid to move or get displaced. The displacement of dentinal fluid stimulates nerve endings in the pulp and hence generates a pain/ sensitivity response to your brain.Hydrodynamic theory
Now the drilling causes heat generation, even though little, due to the coolant, plus pressure and hence causes the fluid to displace and hence pain. This pain usually ends after the treatment.
However the restoration placed, you should have specified which restoration- silver coloured (amalgam) or the tooth coloured. These again have chemicals. These chemicals can penetrate through the tubules to the pulp to elicit a painful response even after the treatment. To prevent this, a liquid known as varnish is applied which acts as an insulator. Also if the infection is deeper, a base or other material depending on the type of restoration is also applied to prevent other stimuli. Varnish and bases
So either there may be a failure in these insulating materials or your pulp may require some time to heal from the procedure. It may have got healed by third or fourth day, if it was due to procedural trauma. In either case you should contact your dentist.
Hope I have solved your question :)
References have been given in the parentheses