OUCH! Tooth hurts after fillings! WHY?

I suggest you call the Dentist that placed the filling and find out if it was a deep cavity. If it was deep, there may be other issues that the Dentist will need to help you with. Other causes could be that you are clenching or grinding on that tooth and making it sore. Your best bet is to see your Dentist so that the problem can be fixed before it gets any worse.