4 days old and milk still hasn't come in-help!

Katie
So my son is 4 days old and my milk still hasn't come in and he's lost a lot of weight. We had to start supplementing with formula just to get his weight back up. But I was wondering if there is anything that I can do to help my milk come in? My boobs are starting to hurt around the milk ducts and feel like they are getting a little bit heavier but I'm not sure. We still feed for at least 15 minutes on each side before we give him a bottle because I don't want to give up on breastfeeding..... I'm just at a loss and don't know what else to do. Any advice is greatly appreciated! Thanks!