The reaction after urination is normal and is the result of them trying to spread their scent to mark their territory.
As far as the mating behavior, it can be simply a sign of dominance but if he is not neutered it could also be a mating action. Getting him neutered can help with this behavior
How do you know it is yeast? It could be something else if a culture has not been done, and if the vet didn’t look at your dog, she sure didn’t do a culture. I wouldn’t try to treat this condition in a hit or miss manner, I would find a vet that will really look at my dog, do a culture to discover if it is yeast, a skin scrape to make sure it isn’t mange, and then make a proper diagnosis.
Oh, in the mean time, get your dog onto a grain-free diet – if it is yeast the grain-free diet may help greatly!