Hi!
Welcome to HCM!
Blood in urine is called hematuria and must not be ignored specially at your age.It may result from bleeding anywhere along the
urinary tract.
Infection of the urine,stemming either from the kidneys or bladder, is a common cause of hematuria. Kidney and bladder stones can cause irritation and abrasion of
the urinary tract, leading to microscopic or
gross hematuria.
Trauma affecting any of the components of the urinary tract or the
prostate can lead to bloody urine. Hematuria can also be associated with kidney
disease, as well as hematologic disorders involving the body's clotting system. Medications that increase the risk of bleeding, such as
aspirin may also lead to bloody urine. Lastly, cancer anywhere along the urinary tract can present with hematuria.
If the repeat test after course of antibiotics gives blood then you must go for further evaluation including ultrasonogram.
Hope this helps!Take care!