Ohhh mama, I had this din after giving birth kaya naiintindihan ko! A few of us sa group namin had rib cage pain postpartum, one said it was from the way baby was positioned, another from how our ribs shifted during pregnancy and it takes time to settle back. But honestly, since it's localized on one side lang, I'd suggest having your OB check it out just to be safe, especially if it's been bothering you for a while or if it's getting worse. Better safe than sorry talaga, and the doctor can rule out anything else and give you proper advice on what you can do to manage it!