There are a few reasons this can happen. The first day or so after your crown prep appointment may mean a sore jaw from holding your mouth open, sore gums near the injection site when the dentist numbed the area, or a sore tooth due to the work done. Sensitivity that continues is most likely caused from the temporary being a more porous material, meaning hot and cold temperatures get through it easier.
Not everyone has this issue, but for those who experience it, little can be done to make it feel better. However, at your appointment, your dentist will tell you to try to avoid chewing on the side of the temporary, or to drink through a straw while one is on. Another reason could be due to the seal of the temporary. During the crown prep, your gums become irritated around the tooth being worked on, which is normal, but causes them to become slightly inflamed. Once the gum tissue settles back down a couple days later, that can cause a gap between the temporary and your gums, creating a small gap in an area or two where temperatures can get in and irritate the tooth underneath.
Be sure to call your dentist if you have sensitivity with a new temporary crown that lasts longer than three days. Your new dental crown will be a much stronger material and temperatures will not bother it at all. It will also have a perfect fit thanks to the impressions your dentist took at your crown prep appointment.