Why do I have hot and cold sensitivity where I had a wisdom tooth extracted?

That's Unusual. If you have temp. Sensitivity around an extraction site, it's most likely the next tooth over. It's unlikely that your sensitivity is coming from the extraction area itself. Generally, this is caused by a little bit of gum recession on the neighboring tooth during the healing from the extraction. This exposes part of the next tooth's root, which can be sensitive. It's generally easy to fix.
Several possiblities. First the root of the tooth in front of the extraction site may be exposed resulting in insult to the central tissues of the tooth. There could be decay on that root or an injury from the extraction procedure as many surgeons use an elevator for removal that depends on adjacent root as a lever point. Lastly, keep this site clean. Return to the dentist, have an exam, and x-ray if it persists.