Is your upper back stiff and tight from sitting at a desk or breastfeeding?
No posture is a bad posture but if you stay in one position for any length of time it can lead to tension through muscles, fascia and nerves.
The movement in your upper back can have an impact on your breathing, pelvic health, shoulder and neck movement.
Try this short video to get you moving and help with discomfort. If your pain persists then seek the help of your local physio or GP.