The thick neck on one side of breastfeeding may be caused by exerting the muscle on one side for a long time, so you can breastfeed on both breasts in turn. When breastfeeding for a long time, the sternocleidomastoid muscle on the same side will be stressed for a long time, the muscle will become thicker, from the appearance of one side of the neck will become thicker, at this time, you should pay attention to rest, and change the direction of breastfeeding. After breastfeeding, you can massage one side of the muscle, or adopt the lying down breastfeeding method to avoid the stress on one side of the neck as much as possible, which may improve the symptoms. If you are breastfeeding on one side of your neck, we recommend that you go to the hospital for a checkup to determine the cause of the problem, and then treat it under your doctor’s supervision.