Collarbone pain can occur due to muscle strain, poor posture, lifting heavy objects, sleeping in an awkward position, minor injury, arthritis, or inflammation around the shoulder joint. Sometimes pain from the neck or shoulder can also be felt near the collarbone. Orthodex MR contains pain-relieving and muscle-relaxant medicines, but its safety during breastfeeding depends on the exact ingredients and your medical history. Since some muscle relaxants may pass into breast milk and cause drowsiness or other effects in infants, it is best to consult your doctor before taking it while breastfeeding a five-month-old baby. Seek medical advice if pain is severe or persistent.