What Causes Lack Of Appetite, Colic, And Extreme Fussiness In An Infant?

Hi , i am a mother of 5 months old baby girl .. i am unable to understand what bothers my daughter .she always cries . from the last 5 days she is not taking feed ... she is exclusively breastfed baby but she is never gets happy after feeding since birth .. Since 6 days she has become extra fussy