Breastfeeding

At the hospital I made the decision to not breastfeed but I think I’ve changed my mind... my sons 3 days old today and my boobs are starting to hurt & colostrum or milk is coming in. With my first my milk never officially came in and what little amount I had took a week to come.

If I decided I wanted to pump and feed is it to late? Will it upset his belly since he’s been on formula?