its quiet normal after such a large litter as the uterus takes time to get back to normal.
i can understand your concern about pio, my 11 month old pup had open pio after her first season
luckly she never got ill with it the only way to tell was because the discharge she had,
she odviosly ended up being spayed.
pio shouldnt be under estimated like buttermilk said it can be deadly in a short space of time.