I do not recommend using this product while breastfeeding, as it contains several essential oils that can be absorbed by the body and get into breast milk. In fact, we don't know how much of this product is absorbed and then secreted into the milk, so we don't recommend it.
When breastfeeding, we'd look to use massage instead and make sure our posture while breastfeeding is perfect in order to relieve soreness and avoid creating new ones. Tylenol™ Extra Strength can also be used without issue.