I have had kidney stones since 1997. Blood in urine can be microscopic or may not show up at all if the stone itself is not moving. Best advice is to see a urologist. They can order a CT Stone protocol if they suspect a kidney stone. If you cannot get in to see a urologist, go thru an ER and tell them that is what you think is going on and what your previous Dr. has said and you have had no relief. Unless a stone is of a descent size, it will not show up on xray. Good luck!
It's possible for extreme constipation to give you HORRIBLE pain. So your dr may have mentioned stools because it can be a cause of pain. If your poos have been bad lately may think about trying a natural laxative like prune juice to get yourself moving- any improvement?
I'm unsure if a kidney stone can be small enough to not cause blood in the urethra but enough to cause pain. It sounds possible, but I think an xray would have shown it. Honestly I'm not very sure though so that's just a guess.