Sounds like you may not be eating enough to support the activity level you are doing and the increased production needs of your baby so your body is holding on to maternal energy stores instead of using them. This article will explain more about that and help you determine how to adjust your plan to allow your body to use maternal energy stores. Some active, breastfeeding moms need 2500 or more calories a day and many find as long as they are making healthy choices, they can't eat too much -- the more they eat, the better their metabolism and milk supply. Give this article a read and let us know what questions you have.
Getting Back to Your Pre-Pregnancy Weight While Breastfeeding babyfit.sparkpeople.com/articles.asp?id=99