Female dogs come into season generally twice a year although it can vary between breeds. The length of pregnancy in a dog is only 9 weeks. All dogs whether they are pregnant or not experience the same hormonal changes (unless they have been neutered). So, for those 9 weeks after their season some will get inappetence and nausea (just like morning sickness in people), others may nest and, in some instances, they may produce milk. Perhaps this is an evolutionary development so they can help suckle other puppies in the pack. These changes usually pass but in extreme cases we can use hormonal supplementation to stop the phantom/false/pseudo pregnancy.
Lucy Travers BVSc CertAVP MRCVS Highfields Vets