Suddenly less breast milk may be caused by lower prolactin level, milk stagnation, malnutrition, lack of sleep and emotional stress. 1. Reduced prolactin levels: During breastfeeding, you may become pregnant again due to insufficient contraceptive measures, which increases the level of estrogen and progesterone in your body and inhibits the secretion of prolactin, resulting in the mother’s inability to maintain normal lactation and a decrease in breast milk. 2. Milk stagnation: During breastfeeding, not paying attention to the cleaning and maintenance of the nipple area, improper breastfeeding, too little milk intake of infants and other factors lead to milk stagnation, blocking the mammary gland ducts, breast milk can not be discharged, so breast milk will suddenly become less. 3. Malnutrition: During the breastfeeding period, mothers eat less, eat food with low nutrient content, or suffer from indigestion and nutrient absorption disorders, resulting in malnutrition and a lack of various nutrients to synthesize breast milk, so breast milk suddenly becomes less. 4. Lack of sleep and emotional stress: prolonged late nights and lack of rest during breastfeeding may lead to endocrine disorders, reduced prolactin secretion and reduced milk synthesis; emotional stress, stress, tension and anxiety may also affect milk secretion, leading to a sudden decrease in breastmilk. Sudden decrease of breast milk may be related to a variety of factors, it is recommended to consult a doctor for a clear diagnosis.