This site goes over signs your dog is pregnant
Dogs are pregnant for about 58-65 days, or about 9 weeks counting from the first mating.
You can read more about pregnancy and whelping in dogs here
You may see a sticky clear discharge around week five or so indicating pups are present in the uterus.
Dogs don't start to get big until the last three weeks of pregnancy so you might only see the vulva staying a bit bigger and the nipples protruding more than usual at this stage.
These sites go over the whelping process in pictures
Hope this helps you!