Sorry for your loss. It's bad enough when you lose them when they are old, but when they are just starting out, it's got to be rough.
I've been very lucky, all my dogs have lived at least close to 12 years, and one past 14. My present dogs are almost 9 now, and every so often I think, "In three, maybe 5 years, they'll be gone!", and get upset.
My friend lost his Doberman pup a couple months ago, he got pneumonia, and never seemed to shake it. He got better for a while, and then it came back, the third time, he died right after he went back to the vet's office after he had just come home a few hours earlier. The breeder paid for an autopsy and they didn't see anything that would indicate there was anything abnormal. He has a new pup now, the breeder is a friend of the family, and she gave him a pup that she had originally intended to keep herself. He's a real handful right now, and is one of my dog King's best buddies. He's about 5 months old now, and is going to be a big one, judging by the feet on him. He's taller than King already, and about as long. Hopefully, he won't be nearly as stubborn as King is, but he looks like he just might be another "Evil Genius" like King is, but about twice as heavy a one.
Anyway, best wishes and sorry again.
