Liz Buchanan BVSc MRCVS
I am curious as to what they tested the urine FOR. When you say that everything was fine, did they not find blood in the urine or is it obvious when you see the per? It sounds from here as though they haven't yet ruled out lumps within the urethra, ureter or the bladder, bladder stones, kidney stones or other causes of spontaneous bleeding from the kidneys, but I can't see your notes and therefore may be wrong. Your vets may be able to see more using ultrasonography or radiography, perhaps with contrast involved - your vet will have a clearer picture than I of what options they have available to them at the present time if they want to visualise the bladder / urethra. Clotting disorders are always worth consideration in unanticipated bleeding, although often other body-parts also show signs.
Obviously you have been working closely with a vet; what next steps have they suggested at this time? They may well have a plan going forwards, even if that plan is simply referral to an expert eg for imaging.
It sounds to me as though you have a lot of questions for your vet, perhaps about what has already been ruled out and what should be ruled out next.
Best of luck - I would love to hear how this case resolves if you feel like coming back to let us know when it is.