Quiz 6 - Infant with large head

This 3 month old boy was brought to the hospital with history of increase in the head size over last 1 week. He does not have altered mental status, seizures, weakness or vomiting. He was born at home to a 30 year old G3P2 mother vaginally at term. He is exclusively breastfed and immunized till date. He lives with his parents in a joint family with 21 members including 11 adults and 10 children. 

Question: What is the diagnosis ?