Child Having Closed Meatus Post Urination, Had Surgery, No Improvement With Various Treatments. Suggestion?

Hello, My son is currently 5 1/2 years old. It started about a year & 1/2 ago where we noticed blood in his underwear , Urology Dr advised of a small meatus and he needs a surgery . We did that but we noticed after the surgory that his meatus keeps healing & closes after he urinates. we went to the Dr again where he advised to use Chap stick & vasiline, we used that for many months with no improvement, the Dr ran out of options. We went to another Dr. where he suggested a follow up surgory, that was done but with no improvement. He suggested another one which we did without any improvement. Even as of now, he has the same problem where after he urinates withing less than an hour, his meatus closes & either we have to open it by hand or the urine force it to open. We tried a 3rd urology Dr and he was puzzled & didn t know. I tried a plastic surgion & she was puzzled. Any ideas & help.