Good day girls, I'm already just about at my wit's end, the baby is not…

Good day girls, I'm already just about at my wit's end, the baby is not eating well, we're on IV feeding, we eat Nutrilon Premium almost from birth, the first two months gained up to 700 grams, in the third month only 400, plus we treated dysbacteriosis, thought it was because of this that he doesn't eat well, but still eats 60 grams and all, starts spinning, throws up the bottle, sometimes he can even eat 120 grams but it's rare, and we had a gastrointestinal doctor visit, and all the tests have been done, in general, there's nothing wrong, I don't know