Since you took him to the vet, I think we can discount a urinary tract infection, which is a typical winner in the ‘why is dog is suddenly pissing the house?’ sweepstakes.
When you say ‘urinating uncontrollably’ what exactly do you mean?
Is he just running around lifting his leg indiscriminately? Is he simply failing to ask to go out and peeing where he happens to be when the need arises? Is he sneak peeing when he knows he is unobserved? Or does it seem as though he is unaware of the fact that urine is running out of him?
Is this going on non-stop or are there specific times when he is more likely to pee the house?
Post again with details and I will do my best to repond.