my dog has swelling under his anus

My dog, an adult dog over eleven years old and unneutered, has swelling under his anus. It is not the perianal glands, but lower down, almost reaching his testicles. The swelling comes and goes with no apparent triggering factor, and varies in degree. From what I read, it could be the retractor penis muscle, but I'm not sure. The vet told me at one of his last visits that the dog could be suffering from prostate problems due to his age and not being neutered, but recent health issues with the dog emptied my pockets and paying for a new consult won't be a possibility until the end of the month. Thank you very much in advance.