What they said ^.
I've spent more time in the dentist's chair than most during the course of my adult life (dental accident as a child) and ninety percent of the time when I've had problems like yours, the discomfort goes away after a day or two. If it doesn't, then go back to the dentist.
You have to remember that although you can't actually feel any pain whilst the dentist's drilling and all that, your tooth, gum and jaw are undergoing significant trauma - sometimes almost as much as if someone had punched you in the mouth. There will inevitably be bruising around the site and, just like anywhere else on your body, it may be sore for a while.