Should I Be Worried??

Olivia • 22 years old, single momma 👣 Dominic A. was born April 28, 2016 👶🏼
My son is 4 days old, and he was getting a mix of formula and breast milk for the first two days (I wasn't supplying enough). My milk finally came in yesterday so all he's been getting is my milk. He's been peeing a lot, which is great, but he hasn't had a poop since the 30th, and it was green and runny like it should have been. He's not constipated, he's passing tons of gas and he's eating/playing like normal. He has had literally no change except no poop. He is my first, so I want to make sure it is actually a concern before I call my midwife