Dog loss appite and very picky with food?

my dog gave birth and she is picky eating now. she tends to perfer i hand feed her and only likes some stuff if she dont like it she spits it out. this has happen 2 another of my dogs but she tends to lose her apitie for no reason in her case its prob metobolic probs. i took the nurseing mom 2 the vet cus i though she got milk fever and the did a profile 3 initial veiw ans additional veiw to see if there was something in her like a pup or pancita they also did a vaginal exam to check her uterus and also cleaned out her anal gland. another thing they did was S.C fluid therpy cus i told them how she was eating. so im wondering do dogs sometimes act diff this seems 2 ber hertetery or something cus it happen to her mom and aunt so what are you comments