An 8-month-old puppy cannot get pregnant. Dogs only enter their first heat cycle, or "season," between 6 and 24 months of age. They can only get pregnant during that cycle.
It's very likely that your puppy is not pregnant, and there might be another explanation for her changes in behavior or appearance.
If you are concerned about your puppy's health, it's important to contact a veterinarian immediately.
They can examine your puppy and determine the cause of any changes, whether it's a medical condition, a behavioral issue, or even something else entirely.