i too hope this was an accident as a resposible breeder would already know the answers.

But ussually after 3 weeks you should be seeing her teets start to swell, her tummy should be just starting to get chubbier. Dogs are ussually pregnant for only 58-66 days after mating.
As soon as you suspect a pregnancy you should go to the vet for an exam, they can answer any questions you have, it is good for the vet to become familiar w/ the pregnancy just in case any complications occur.

also you mommy dog should be on a good quality puppy food now, it has more nutrients in it that your dog will majorly need.

I hope you get the male fixed asap & the female spayed right after the pups are weaned.
Good luck, any more questions just ask!!!