My bulldog urination problem my bulldog cant pee

My bulldog urination problem my bulldog cant pee

Please help me save my bulldog Zues.  He’s always been sickly and is literally allergic to everything. Several weeks ago he started having problems peeing. He can only get a few drops out at a time. My vet has run X-rays, ultrasound, blood and urine test and they can’t figure out why. No antibiotic helps. He’s suffering so much I’m going to have to put him down if we can’t find an answer. Do you have ideas? Thank you so much.