1997 Buick Century EGR valve

Engine Performance problem
1997 Buick Century 6 cyl Front Wheel Drive Automatic

we have a 1997 buick centur, for the past two years we have had to buy a new egr to pass inspection, after about two weeks the engine ligt comes back on. I know now that it cant be the egr valve because they are new and have not reached the mileage limitations on the product, plus we only drive the children to school, or use this vehicle to grocery shop. We probly dont even put 10,000 miles on the care in a years driving. We know the diagnostics says the egr, but it has yo be somthing elsethat makes the engine light return after only a weeks worth of driving. Can you give me an opinon of what may be causing this.