Most common cause is stones in kidney which is blocking
urine pathway. Other causes are changing sexual partners frequently,
pregnancy, diabetes
and of course childhood infections. The urine can also be due to retention of urine anywhere in its flow due t obstruction. The obstruction can be due to abnormality of structures since birth, stones.
So you should get a ultrasound, CT scan done and also some urine and blood tests. Avoid taking pain pills. Drink about 2-3 liters of water in a day.