From formula to Breastfeeding

Ok my son has been in Nicu for 2weeks due to feeding trouble, but he was discharged on yesterday. They had him drinking 2oz every 3hrs around the clock which resulted in dirty diapers with no problem. I finally got to introduce him to breast milk yesterday and today and now I'm not sure he's getting enough because he will nurse for almost 10min then the next feeding nurse for 30. He also hasn't pooped all day since early this morning. Idk if I should go back to pumping his 2oz out or what 😕