Hi, A few years ago I had the same problem, blood in my urine, I was tested at the doctors using the test strips and I had signs of kidney issues.

Was sent for scans and it showed a 3 stones, whilst waiting to see a consultant I passed one, oh hell it hurt, worst pain I have ever had.

Stones are sharp and look like coral and as my doctor said it is the sharpness of the stone that cuts the kidney hence only small amounts of blood.

May I also suggest the you get your prostate checked, it is a quick simple procedure a PSA blood test and a digital rectal examination, the digital exam is just uncomfortable not painful at all.

I know I lost my dad to prostate cancer so I have mine done every year.

Hope this helps
Ian