In addition to the increase of blood in my urine, I had periodic pain with urination.
I also had a stabbing pain between my rectum and mu scrotum. This was later discovered to be due to the location of my cancer. It is at the right ureter junction which shares a nerve with the area I just described.
My signs and symptoms were very similar. My first cystoscopy was negative as well. About a year and a half after the first cystoscopy, I had a CT and another cystoscopy that led to the eventual cancer diagnosis.
As suggest earlier by Sara Anne, I would return to your urologist and have them look again.