My Tooth Hurts While Eating After a Normal Filling?

It sounds like there may be a gap between the bottom of the filling and the tooth. If this is the case then a new filling to seal that gap may help significantly. If there is a crack in the tooth then redoing the filling will likely not help and a crown may be needed. 

It is difficult to answer this question without an xray or exam, but sometimes, simply replacing the filling may solve your problem. Tooth colored fillings are extremely technique sensitive and if not placed properly they may result in post operative sensitivity. If the filling is too bulky or not touching the adjacent teeth you may be getting some gum inflammation since it is a food trap and that may cause the ligament around your gums to get inflamed and cause some sensitivity when chewing. There are a variety of reasons why your current filling may be failing.  If you are not sure about your current dentist you always have the option of getting a second or even third opinion.