Aiyoh, that sounds uncomfortable lah! Back and shoulder pain with breathing discomfort can be a few things, bisa tension from posture, especially if you're carrying baby or doing a lot of lifting, or sometimes it's something that needs checking out properly. I'd really suggest popping to see your doctor or even a physio to rule out anything serious, because breathing issues combined with back pain isn't something to ignore. A few of us mummies had similar issues and it turned out to be muscle tension from how we were holding the baby or hunching at work, once we fixed the posture it got better, but better safe than sorry lah!