Ay, common yan sa newborns actually! A few of us mums experienced the same, parang may slight swelling sa chest, diba? It's usually just hormones from pregnancy passing through baby, or sometimes just normal newborn development, pero definitely best to mention it sa pedia mo sa next checkup para ma-confirm lang na normal lang talaga at walang ibang concerns. Hindi mo kailangang mag-alala ng malaki, pero better safe than sorry with babies, so definitely let your doctor check it out.