GROSS HEMATURIA AND RIGHT FLANK AND BACK PAIN FOR 8 MONTHS

i have had gross hematura for many months, right flank and back pain, no infection, per several cultures, an ultrasound this week did not show any tumor, mass or stones.
can anyone suggest what may be wrong? the pain in flank and back is constant, then every few weeks i will develop a burning in the bladder area and urines turns very dark for days, then urine clears up and pain in bladder goes away, but flank and back pain stays constant.
can anyone give suggestions?

[Dr Santos]

How are you? Can you elaborate more on the color of your urine? Was it dark brown or tea-colored? Are there other symptoms present? Were they able to test your kidney or liver  function? Some liver disorders, especially hepatitis and cirrhosis, and the rare hereditary disease tyrosinemia can turn urine dark brown. So can acute glomerulonephritis, a kidney disease that interferes with the kidney's ability to remove excess fluid and waste. It would be good to eliminate these causes for us to reach a diagnosis.

Take care and keep us posted.