My male cat had that problem and we almost lost him to it, didn't know he was that sick until he peed blood in the kitchen. I was told that the only way to ensure he didn't become blocked again was to have him given the Perineal Urethrosotomy ("During a perineal urethrostomy, the penis is removed and the wider diameter pelvic urethra is opened and sutured to the surrounding skin, creating a new permanent opening in the urethra, just below the anus.") He also had bladdery surgery but because a not-very-smart-vet got a catheter stuck in there and it tore off when they tried to remove it.
I don't know if this would be mentioned to anyone else by a vet, but it worked wonders for my baby, he has had no problems since then. Am so sorry for your baby and will pray for him
and for you and your pocket book