Did the vet mention bladder stones? It sounds like he might have a urinary tract infection. When this happened to my senior small breed, he was treated with antibiotics and seemed to be okay, then the symptoms started all over again a few months later. When they did a x-ray/ultrasound it showed he was loaded with stones and needed emergency surgery.
So, if it was my dog I would get the ultrasound done now so that you will know what you are dealing with. Was blood work done? He’s due for a good senior workup, imo.
/forums/search/bladder+stones/ per the search engine here
