I did a search for another member several weeks ago. It yielded a whole bunch of medical sites that talked about this. There are many reasons for blood to be in the urine. One of which is an infection. Infection of the bladder or infection of the kidneys. Usually other symptoms accompany the blood in the urine. I would suggest you see your GP or a urologist for help while you keep searching the internet. Best wishes for a quick recovery.
I agree with Artdude, a consultation is in order.
Blood can come from anywhere along the tract, hence diseases of the kidney, the ureter, the bladder, the prostate, the urethra.
Common reasons would include stones along the urinary tract and urinary tract infection. Less common causes would be malignancies involving any organ along the tract, diseases of blood and blood clotting, and immune-related disorders that damage the kidneys.
Investigate also if it is really blood. Some patients who are taking certain medications may have urine discoloration and think that they are bleeding. Some drugs that affect blood clotting of course may produce bloody urine as well.