There can be a difference between a Urinary Tract Infection and a blockage. He could just have a UTI and need an antibiotic. If your boy is developing crystals, he could eventually block up (males are more in danger than females due to their different anatomy). Just a heads up...not saying this is your boy now..but a male cat constantly going in the litter box with no results, needs to see a vet as soon as possible! Permanent damage can be done to the kidneys if you wait longer than 24 hours. Observe him closely when he goes into his box.
Your best bet if your kitty isn't in immediate danger, is to get a urine sample tested as soon as you can.
Caretaker of 2 dobermans,, 1 schnauzer, 5 cats, 3 goats, 1 parrot, 1 bearded dragon lizard, 11 chinchillas.
Rest in peace, Cricket, Casey, Bella, Yank, Chloe and Bones.