I am worry about my 5 months old baby has not poo for 4 days. Should I take her to see doctor?

Since baby is still young and not able to take fiber diet from fruits and vegetables, you may feed your little one with GAIA probiotics drops to ease the constipation. You can purchase it from Guardian or Waston. Remember to store in fridge after every use. Also, you can try to do baby massage to ease the constipation. Example of baby massage can be found in youtube: https://www.youtube.com/watch?v=RWFg0ODAQvE