My baby's first formula is s26gold then at 5months i switched to similac then she is 10months old now i want to switched it back to s26 gold two 6 to 12months because she is constipated everytime she poop and as i notice shes not gaining weight?

Screening/weight : The reason for her poor weight gain should be investigated. The number of ounces per day can be kept as a record. Her height and weight chart may be reviewed by your pediatrician. Lab testing may include a thyroid panel, complete blood count and metabolic panel. Switch to whole fat cow's milk as tolerated or lactose free milk, a small amount of prune juice may help to relieve the symptoms.