Constipated baby and throwing food up 1 month old

My friends baby has had a long journey. He had surgery when he was first born and then stayed in nicu for a while. He had a very low chance of making it. But he’s a month old and he’s been constipated constantly she gives him everything she can to help him poop but she doesn’t like how he relies on it to go. What are some natural ways to help. The other thing is he keeps throwing up after every feed. He eats about 4 oz and they went from breast milk to sensitive to how soy and he is now starting to throw up again. Any ideas of what she can do to help him keep his food down? She calls the pediatrician and they haven’t been very helpful they keep saying it’s normal and stuff. So please any tips or advice she’s a first time mom!