Lack of poop

Kathleen💙💙Twin Boys

Hello my son is two weeks old and formula fed with a high iorn formula due to being born early. It’s been a few days since he pooped, the last one was gigantic and soft. I’ve tried tummy massages and gentle bicycle legs the last two days, but he’s not budging. His brother has no issues going, and I have an email in to his doctor. Any advice to get him going that has worked?