esophogus colitis

my 12 year old grandson just had surgery on june 3 the doctor called it flipping his stomach now he doesn't know when he has to pee. he can pee some when we tell him to go he drinks good but just doesn't pee  a lot and only when we tell him to. we took him to the er they did a scan and said his bladder was holding 123 ml of urine and said they did not feel it was related to the surgery and sent him home untreated. we don't have a clue what to do. we requested a urologist but can't see him until august 4 that's almost two months away. he eats good, drinks plenty, what can we do HELP