Different results in different reports.

I am having a good amount of post voidal residual urine (with constant urine dribbling in my underpants) (i can also feel that urine is hanging there but not coming out and when i stand approx a  teaspoon of it falls out) along with burning sensation after passing the urine I got urine routine and culture but getting different results In the first report both routine and culture were ok In the second report the routine was normal but in culture I got e coli The third routine showed bacteria and in culture got kiebsiella I got 500 mg amikasen injection twice a day for 5 days for kiebsiella and drank k-mac uti for e coli. After 10 days i again got the test done This time in the first report both routine and culture were normal And in the second report routine was normal but in culture got e coli. I have been to both gynecologists and urologists but haven't found a concrete solution