Gastroenteritis: This is the most common cause of green stool in infants, often due to a viral infection. The harder to settle behavior could be related to discomfort or pain associated with the infection.

Food Intolerance or Allergy: Introduction of new foods can sometimes cause changes in stool color and consistency, along with fussiness in infants.
Teething: While not directly causing green stool, teething can lead to increased saliva production, which may change stool consistency, and the discomfort can make the child harder to settle.
Overfeeding or Foremilk Imbalance in Breastfed Babies: Can lead to green, frothy stools due to the high lactose content and may cause discomfort.

Intussusception: Although less common, it's a serious condition where a part of the intestine slides into an adjacent part, potentially causing bowel obstruction. Green stool can be a sign, along with severe abdominal pain and drawing up of the legs.
Pyloric Stenosis: Typically presents with projectile vomiting, but in some cases, can lead to changes in stool due to decreased feeding and subsequent dehydration.
Infectious Diarrhea (Bacterial or Parasitic): Certain infections like Salmonella or Giardiasis can cause green stools and significant illness in infants.

Cystic Fibrosis: A genetic disorder that can lead to malabsorption and changes in stool, including green color due to undigested fats.
Biliary Atresia or Other Liver Disorders: Can cause changes in stool color, including green, due to issues with bile production or flow.
Congenital Sucrase-Isomaltase Deficiency: A rare genetic disorder affecting carbohydrate digestion, potentially leading to abnormal stools.