Talk to Gastroenterologist on No Stool Passing

Hello Doctor, My son is 21 days old (born on 24th April). He has been on breastfeed since the beginning but 3 days (Wednesday) ago I gave him 2 ounce of formula and then 2 ounce again on Thursday. He pooped on Thursday Morning but ever since then he hasn’t pooped at all. On Friday i gave him no formula only mother feed but still no stool till today. Before Thursday morning he use to poop everyday but bow I’m worried as its been 3 days and he hasn’t pooped. He passes gas, has almost 8 wet diapers & takes feed normally but grunts and has a discomfort sleep since 2 days (which I’m guessing is because of stool). Kindly guide as to what is the reason behind him not passing stool and how can it be resolved?