Constipation

This is my third kiddo I shouldn’t be concerned but my sister has now put it in my mind that their could be something wrong with my lil girl’s intestines. She is 6 weeks old so just over a month and a half. She was having that seedy yellow poo and than all of a sudden she has stopped pooping. Her last time pooping was yesterday afternoon. Is there any helpful ways of seeing if it’s true constipation or if something is truly wrong internally. She is passing gas and burping. I know about the massages and the bicycle movement as well and the juices. Just need to see if I’m missing anything. Thanks