I just wanted to encourage you and let you know it is completely safe and natural to lose weight while breastfeeding. The thing you want to avoid is the type of "diet" that would cause a rapid and significant weight loss. The good old-fashioned "watching what you eat" and walking 1/2 an hour a day should do it (breastfeeding itself burns over 600 calories a day!)
I lost my weight by learning about calories. This seems obvious, and sounds boring, but I learned tons and majorly enjoyed the (safe-level) 2 lb. loss per week I experiended! You might be surprised how many extra calories some of your healthy foods are packing into your total each day. Learning which healthy foods you can eat tons of, and finding some healthy low-cal snacks, is very helpful! Also, taking a quality fish-oil supplement may help--and it's excellent for your baby too! Here are some links. . . good luck--and don't let your body-worries stop you from nursing your precious baby!
Book on Amazon: http://www.amazon.com/gp/product/0345492595/ref=cm_cr_asi...
Helpful website: http://www.kellymom.com/nutrition/mom/mom-weightloss.html
Fish oil info: http://www.bestsyndication.com/Articles/2006/q/quinn_mars...