He shouldn't be getting this call your vet. They are really tired after parvo, and need to be eased back onto food. Their poos should normal colour but a little soft is ok. Parvo causes the inside layer of the intestines to be stripped and come out in their diarrhoea so its looks like snot from the kids nose. It then starts to bleed. Blood now after its finished could possibly be bacuse the food he is eating is irritating the already damaged intestines so the vet might want to give him some prescription food or give his body another day or twos rest before eating again. Just note also, parvo survives in your house and yard for 2 years so make sure any puppys coming onto your property are vaccinated and preferably kept away from where ever your puppy was as well. On top of this Dobermans and Rottweilers are super sensitive to parvo so probably discourage them from being on the property. Remember this virus can kill and is very expensive to treat in severe cases so better to be safe than sorry. But call your vet - hope this helps.