Back and neck pain can be caused by a number of factors when nursing a baby. As you recover from childbirth and pregnancy, hormonal and physical changes might cause pain, swelling and unease in your ligaments. In addition, your body takes time to readjust to the forward weight distribution of the baby in the womb after pregnancy. The most common cause, however, is improper posture and repetitive nursing positions used every day during feeding. This is what leads to pain in the shoulder blade region, back, and neck.