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 now and weighs 5.7 kilograms. The breast milk is clearly insufficient now. I've given the baby formula, but he won't drink it. I bought B&B, but he still refuses to drink it. I then bought Dumeizhi, but he keeps pushing it out with his tongue. If I try to feed him again, he starts crying hard.
When I gave him probiotics for over a month, he would eat them, but now sometimes he does. However, he vomits shortly after eating.
Previous Treatment and Effects:
A health check said he has indigestion.
What kind of help is expected:
I hope the baby can gain more weight.

Doctor's answer:

Babies who are accustomed to breast milk 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. Forcefully starve them a bit; when they are extremely hungry, they will eat. Otherwise, the baby will constantly reject the little bit of milk, making it easy for them to be undernourished and cry, which can also interfere with their growth.
Recommendations: There are many ways to increase milk production. It is suggested 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, and cook soups with pig fat and add vegetables to drink. Chicken soup, etc., can also be eaten. "Milk-enhancing foods" can be consumed appropriately, and fruits can be eaten. It takes effect in two days, and well-prepared milk will continuously increase. Herbal decoctions or acupuncture can also increase milk production. Additionally, the child should be encouraged to suckle more to stimulate milk flow.
Wishing the baby healthy growth. The above advice is for the question "Baby is very thin, not enough breast milk, and refuses formula milk—what should I do?" It is hoped that it will be helpful to you. Wishing you good health!