Crystals causing a urinary blockage in cats?

My baby (my cat, Jack) was experiencing a similar thing to this. He would visit the litter tray every 10 minutes but nothing would come out, except blood. When I went to the vets, they gave him some antibiotics and he was fine. About a month later, the exact same thing happen. So they gave him antibiotics and it went away again. That's about all I can say, but I do feel like the vets didn't/haven't got to the bottom of it all. I do worry sometimes but that's about all I can say. I hope he is better soon. You could try another vet, just to get another opinion. I think its important to get more than one opinion because one ve my have there mid set completely on one thing when itcould be something else. Good luck and try not to worry x