Sounds like you are not eating enough to support weight loss from maternal fat stores for energy. While we totally understand why you don't want to use Babyfit, the recommendations at SparkPeople do not apply. Most breastfeeding moms need at least 1800 calories just to keep up with breastfeeding and typical day to day stuff. If you have great metabolism from regularly working out prior to baby, you will need more than that. Exercise causes you to need more on top of that. Some active breastfeeding moms find they need to eat close to 3000 calories with regular exercise to maintain their milk supply AND slowly lose weight.
This article from Babyfit will help with the explanation why.
Getting Back to Your Pre-Pregnancy Weight While Breastfeeding babyfit.sparkpeople.com/articles.asp?id=99
So, you may want to reset your Sparkpeople program for weight maintenance and get those calorie recommendations and then add 300 calories to the top and bottom of what Spark calculates for maintenance for pregnancy/breastfeeding to give you a starting point. To that you will want to add exercise calories on the days you exercise (usually about 100 per 15 minutes of exercise).