3 weeks and a half child fever stomach pain is considered to be caused by enteritis, acute bacillary dysentery, gastrointestinal cold and other diseases. 1. enteritis: rotavirus, E. coli and other pathogenic infections, in addition, overfeeding, allergies, nutrient intolerance, etc. can also trigger enteritis, the child may appear stomach pain, diarrhea and other symptoms, and feces can be watery, egg drop soup, accompanied by varying degrees of vomiting, fever. 2. Acute bacillary dysentery: it is an intestinal infectious disease caused by Shigella infection, after the onset of the disease, the child will appear chills, fever and other symptoms, and the temperature can be up to 39 ℃ or more, accompanied by loss of appetite, stomach pain, diarrhea and other phenomena, the stools are usually dilute watery stools, and then turn into mucus, pus and blood stools in 1~2 days. 3. Gastrointestinal cold: gastrointestinal cold can also lead to fever, stomach pain, and will be accompanied by nausea, vomiting, diarrhea and other symptoms, in addition, the child will also have varying degrees of headache, nasal congestion, runny nose performance. Fever and stomach pain in 3.5-week-old children may also be caused by appendicitis, acute peritonitis and other diseases, it is recommended to consult a doctor in time to identify the cause of the disease, and actively cooperate with the doctor’s treatment.