Vomiting after breastfeeding in 3.5 months old babies is related to improper feeding, indigestion, acute gastroenteritis, intussusception, meningitis and so on. 1. Improper feeding: some 3.5-month-old babies may vomit after breastfeeding when they are fed improperly, such as being fed too much or too quickly. 2. indigestion: gastrointestinal power disorder, stomach to food tolerance diastolic function decline can cause 3.5 months baby indigestion. Common symptoms of indigestion include postprandial fullness and pain in the upper and middle abdomen, while indigestion in babies may be manifested by crying and restlessness, vomiting after eating milk and so on. 3. Acute gastroenteritis: If a 3.5-month-old baby suffers from acute gastroenteritis, he or she may vomit after feeding, have a fever, diarrhea, loss of appetite, crying and restlessness and other symptoms. The occurrence of acute gastroenteritis is related to pathogen infection and improper diet. 4. Intussusception: Intussusception is related to intestinal peristaltic rhythm disorder, and may also be caused by other factors such as infection and abnormal intestinal development. Intussusception can cause some 3.5 month old babies to vomit after breastfeeding, but also easy to be accompanied by paroxysmal abdominal pain, blood in the stool, abdominal mass, abdominal distension and other symptoms. 5. Meningitis: Meningitis is usually caused by pathogenic microbial infections, and typical symptoms include fever, chills, nuchal rigidity, vomiting, limb movement disorders, and irritability. 3.5 month old baby vomiting after eating milk, there may also be other reasons, it is recommended to go to the hospital, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.