I have a 13 1/2 week old Golden Retriever puppy. Within the last 2-3 weeks she has urinated while asleep 3 times. The vet said that this is not uncommon but I've never heard of this before. Has anyone had any experience with this or know anything about it? A urinalysis was negative for a bladder infection (however, the urine was pretty diluted).

My miniature poodle does this.
She is 2 years old and she has done it since she was a puppy.
She basically has a weak bladder, I haven't heard of a Golden Retriever having it but I am not too familiar with that breed.

My girl does not do it when she goes to bed for the night, but during the day/evening when she is relaxed but not completely sound asleep she does it.

There are medications to help ease it but my vet told me that the side effects are worse than the problem.

I'm lucky in that I have floor boards and when she falls asleep on the floor I can wipe it up and give her back end a rinse.
If she goes on the rug or her bed a put a little soda water on it and dab it up... it neutralizes the odor.

It could be another problem but I am surprised your vet didn't mention this.