I recommend that you see a nephrologist and have a 24 hour urine test for urinary supersaturation index. There are several laboratories that perform this testing including Mayo Clinic, University of Chicago (Litholink), University of Texas in Dallas and others. These tests determine the cause of recurrent kidney stones and suggest ways in which to reduce stone formation and prevent stones from forming. I recommend that you consult with a nephrologist and have such testing performed.
For more information on tests to measure kidney function click here: