A three-and-a-half-month-old baby often cries and becomes fussy before going to sleep at night.

It is possible that a 3.5-month-old baby's crying before going to sleep at night may be caused by hunger, overfeeding, urination, defecation, ear infection, colic, and other reasons. Different management approaches are required depending on the specific situation.

1. Hunger: At 3.5 months of age, the baby's stomach capacity is small and each feeding volume is limited; the baby may cry due to hunger before bedtime. If the baby's last feeding was earlier and the baby shows rooting behavior, finger sucking, or other signs while crying, try feeding the baby to see if the crying can be soothed.

2. Overfeeding: If the baby eats too much before bedtime, it may cause indigestion, bloating, discomfort, and crying. In this case, gently massage the baby's abdomen in a clockwise circular motion to promote gastrointestinal motility and aid digestion.

3. Urination or defecation: The baby may cry due to wet or soiled diapers causing discomfort. Parents should promptly check the baby's diaper and change it if necessary, keeping the baby's bottom clean and dry.

4. Ear infection: Ear infection may also cause the baby to cry, especially at night, as the baby may experience ear pain and have difficulty falling asleep. If an ear infection is suspected, the baby should be taken to a medical facility promptly for examination and treatment.

5. Colic: Colic is one of the common problems in babies around 3 months of age and typically presents as sudden episodes of intense crying, abdominal distension, legs drawing up, etc. Gently massaging the baby's abdomen in a clockwise direction may help relieve intestinal spasms. If the symptoms of colic are severe, prompt medical attention is recommended.

If a 3.5-month-old baby persistently cries before bedtime and the crying cannot be relieved by the above measures, a medical evaluation should be considered to identify the exact cause and provide appropriate treatment.