if you have blood in your urine but no signs of infection (negative for bacteria, no fever, etc) but you have abdominal or back pain and even nausea or vomiting, you probably have kidney
stones. i'm 28, having my first, and
it's no picnic. i was lucky and
my dr. ordered a CT scan
, which definitely showed a kidney stone. but some tests for some people will not show a stone (especially x-rays and ultrasounds).
so if you're experiencing these symptoms, get more tests run.