What should I do if the baby is very thin, does not have enough breast milk, and refuses to drink formula?

Patient's question:

The baby is three and a half months old and now weighs 5.7 kilograms. The breast milk is clearly insufficient now. I offer formula, but the baby refuses to drink it. I bought Bellamy's, but the baby won't drink it either. I then bought Holle, and the baby keeps pushing it out with their tongue. If I try to feed them again, they start crying hard. When I gave probiotics for over a month, they used to eat it, but now sometimes they do. However, they vomit shortly after eating.
Previous Treatment and Effects:
A health checkup said the baby has indigestion.
What kind of help is expected:
I hope the baby can gain more weight.

Doctor's answer:

Babies who are accustomed to breastfeeding have very picky tastes, so they may resist formula milk because breast milk is mild while formula has a slightly fishy taste, making them reluctant to drink it. If you force them to starve, they will eventually eat when extremely hungry. Otherwise, the baby will constantly reject the small amount of milk, making it difficult to be well-fed and leading to crying, which can also interfere with growth.
Recommendations: There are many ways to increase milk supply. It is recommended that you do not overexert yourself and pay attention to rest, as a bad mood is also one of the reasons for insufficient milk production. At the same time, drink more soups like bone broth, eat more greasy foods, such as pork trotter soup, thick crucian carp soup, or soups cooked with lard and vegetables. Chicken soup, etc., can also be consumed. Additionally, you can take "milk-enhancing" supplements and eat some fruits appropriately, which will take effect in two days, with increased milk production observed the next day. Herbal decoctions or acupuncture can also help increase milk supply. Furthermore, it is important to let the child suckle more to stimulate milk production.
Wishing your baby healthy growth. The above advice is for the question "My baby is very thin and does not drink formula milk—what should I do?" I hope it helps you. Wishing you good health!