It's hard to tell if a fish is pregnant because they are sometimes made fat by your loving care.
You should know that the Goldfish spawns eggs. She doesn't have babies.
The female goldfish will be chased by the boys in the tank. It's just the way it is...
If you don't have other fish, that could be a problem because she may not spawn the eggs and they could cause a problem.
If you've have something like Platy's or Guppies (tropical) and you've male and female together it's a good bet that your females will be pregnant, and these do give birth to live young. Most get eaten by the other inhabitants in the tank, but alot will survive if they've somewhere to hide until they're bigger. And the symptoms are the usual- the females look like little barrels.