female dogs can get pregnant as soon as they start going into heat. You may notice small spots of blood on the floor, in the snow etc. That is from your dog having her period, from this point on she can become pregnant. I personally have had a dog that got pregnant at 7 months had her litter and got pregnant right after.
No.
Just like humans, they are carrying life with them. Dogs that are pregnant usually carry a litter of four or more. They are going to eat more to support their puppies.
You don't need to tell anyone if a dog is pregnant, but if you want to, you can tell the dog's owners.
if your japanese spitz is pregnant she will just show all the normal signs in other dogs.
No only a female can fall pregnant with a litter of puppies but if she is desexed then she cant either