How do i know when a dog is pregnant

PHYSICAL changes.
In the final third (weeks 6-9) of pregnancy, the dog’s belly becomes rounded and distended. Her mammary glands start to develop and become more obviously swollen, as they get ready to produce milk.
Behavioral changes.
APPETITE changes.
Towards the end of pregnancy, the dog’s will womb grow larger and take up more space in her belly. She won't be able to accommodate large meals, so she'll start wanting to snack, eating a little at a time more frequently.
NESTING
Watch for nesting. When it is nearly time for her to deliver the pups, the dog may start to nest. [3] She will gather blankets or clothing in a secluded place as she prepares a suitable safe warm environment for her imminent new arrivals.
The exact timing of nesting varies from 2-3 weeks to 2 - 3 days prior to giving birth.