Why does my lower back left side hurt when I drink (only one mixed drink sent me into pain)?

Flank pain . There is a scenario in which there is obstruction to urinary flow at the junction of kidney outflow to the urine tube(ureteropelvic junction). This is dynamic obstruction and when there is increased urine flow, like after drinking beer, the obstruction becomes prominent and cause flank pain. This one of the many possibilities. Kindly get evaluated by a doctor. .