How much weight should a 3 1/2 month old puppy be gaining weakly?

A week ago I was at the vet and he weighed 23 lbs. And today at the vet he weighed only 24 lbs. So he only gained 1 lb in a week!!! Shouldn't a puppy be gaining more weight then that? I told the vet my puppy is to skinny to me. He said that he is not. He felt his ribs and said they feel fine and that they are covered with a layer of fat which is good and he said there suppose to be in a little in the back end. So he wasn't really worried about him not gaining weight but its worrying me!!! So how much weight should a almost 4 month old rottweiler puppy be gaining weekly? Thanks!!!