It's  quite possible  that the stone u passed is just a small fragment that might have been  left at the end of surgery which came out Its quite normal  and NOT doctors fault Stone formation is due to environmental and genetic causes... U should do these all to prevent stone formation -- 2 hourly one glass fluids... water , natural juices, buttermilk etc ... except sugar-rich cold drinks Citrus fruits daily... best is orange, then lemon Salt restriction Weight control Syrup alkalizer ( kcit, potrate mb6, alkastone) 15 ml in 1 glass cold water 3 times a day... if ur doctor prescribes