The earliest and most reliable way to diagnose pregnancy is via ultrasound--this can be done as early as day 20 but more reliably at day 22-26 of pregnancy. Fetal skeletons calcify at day 45 and can be seen on x-rays. This is the best way to estimate number of puppies. Often dogs do not begin to gain weight until 4-5 weeks of pregnancy. At some point uterine enlargement and puppies can be palpated--this depends upon litter size, body condition of the female, and skill of the person palpating. Gestation lasts 63-66 days in dogs. Talk to your veterinarian for further information.
If she has been recently mated, she should start to show, the first sign is usually swelling of the teets. In no time you will know for sure as dogs gestation period is shorter than humans and will show, swollen belly etc. Much sooner
Weiners don't get pregnant, woman do.