Passing stools once in 5 days in 4 months baby is always normal.. do not worry.
As you said baby is active and playful, continue breast feeding every 2 hrly with proper burping, do not use any kind of bottle feeding.
Next Steps
passing flatulence indicates no intestinal obstruction.
Health Tips
mostly constipation occurs if there is a family history of
thyroid hormone problem, so evaluate for hypothyroidism, if father /mother has hypothyroidism.