Go to the vet
If you suspect that your dog is pregnant you should go to the vet as soon as possible. So, you can know the date you will give birth and discuss any necessary changes in medication. On the other hand, your vet could also determine if your dog is having a psychological pregnancy.
Ultrasound machines can visualize puppies approximately at 3 weeks of pregnancy. In addition, the veterinarian can count the fetuses to know the number of puppies in the womb. In this way, you will know if all the puppies are healthy when your dog gives birth.