Wa... Your baby is sleeping very well! 4 hours in the day and 6 hours at night! Have you rest well too? Ok, I dont't have the same problem as you exactly. But when my child was 5 days old, she has this reflux problem and she keep vomiting out the milk I gave. Be it breastmilk or formula milk. Then I start to think that over overfed. Slowly, the problem gets better. She's 3 months old now still have this reflux problem occasionally. But dont't worry, her pediatrician told us that its normal. Cheers!