Yes, some cats are more prone to recurrences. He may have gotten worse even on medication if the medication was not specific to the organism causing his infection or if it does not concentrate in the appropriate tissues sufficiently. Sometimes a vet (or physician) will give a "wide spectrum" antibiotic, but some organisms are resistant, so if the condition does not clear up a culture will have to be done and a more specific antibiotic given. Since he does not show any crystals, it's not likely that he would have a blockage.

Good luck with him and keep us posted.