Hello, and welcome to Just Answer. I'm sorry to hear that Luca is having problems. If there is a blockage in ihis urethra, it would typically be due to crystals or stones. One thing you can safely give at home to help dissolve crystals or stones is cranberry juice or cranberry juice extract. These will help to create a more acidic urine, which will dissolve the most common bladder stones.
It does sound like there is a possibility that Luca has some stones, but your vet should have prescribed something to help clear them. or at least discussed treatment options with you.