hi there. my son is 2 weeks old today but has not poop for 2 days already. I have just changed his diet which is into fully infant formula like 5 days

Dont think he is constipated as he has been farting quite a lot every day. Burping is quite an issue after feeding as he has always been falling asleep while feeding him. Without poop for two days, is this normal for 2 weeks old baby? Need your advice. Am worried. Thank you.