My baby is nearly 4 weeks old. He has been grunting and strainng as well as going red in the face and looking like he needs a poo. While I was BF he pooped every feed, but I’ve recently changed to formula feeding and now he seems a bit more unsettled and has not pooped since yesterday at 3pm, but he has been straining. I’ve been giving him infacol to try and help. What can I do to help him?