Average gestation is between 59-63 days. btw the end of the 1st 4 weeks, u should be able to notice a considerable change in the size of the abdomen and the female dog might become more affectionate in character. there might also be an notable increase in her appetite.

To confirm pregnancy , u can bring to the vet's to either do an ultrasound or an low radiation exposure xray, of which the latter is much more economical although it is still in much debate whether fetal puppies should be exposed to any radiation at all. Another thing to note is that xrays generally only show the skeletal structure of the puppies only after 45 days of gestation.
Hope it helps.