My dog had puppies 9 days ago, it was accidental as she is 7 years old now and had a litter prior that all died within a week. She was booked in for a spay but unfortunately it was too late to do. She had 3 puppies (previously only had litters of 5) two of these puppies weighed 205&210 grams at birth and the third was 170g, upon weighing him the next day he was 154g, he does not have a cleft palate, but wasnt drinking from mama so we were giving him some beaphar formula milk, eventually he seemed to be drinking off mama frequently so we reduced formula feedings. 8 days later I decided to weigh them and he has gained no weight at all, whilst the two others have double in size. He seems healthy, he is warm, active and mama takes care of him, but is so small? What can I do?