E.,
After giving birth, I had a difficult time figuring out what was the appropriate amount of food to eat while breastfeeding and trying to lose weight. Your caloric needs are slightly higher while breastfeeding, so it's possible to eat too little and end up slowing your metabolism down, making it difficult to lose weight. It's also possible to delude yourself into thinking you can eat a lot more than you should just because you're breastfeeding.
I decided to join Weight Watchers online, and I was back at pre-pregnancy weight (I gained 45 pounds during the pregnancy!) approximately 7 months after giving birth. I've maintained the weight loss for over 9 months, following the Weight Watchers plan (not perfectly of course, but doing the best I can.) Doing it online is very helpful and easy to do when you have a baby. I take about 5 minutes each night to plan out the next day's meals. I'm also a vegetarian and do not eat any sugar. But sometimes even vegetarian food can be high in calories...especially when portion sizes are out-of-whack.
Also, try not to think of this in terms of going on a "diet." Think of it as a lifestyle. Remember that you want to keep the weight off--there is nothing more humiliating and demoralizing than losing a bunch of weight only to immediately regain it back. Been there, done that--haven't been on a "diet" in years and years. So have a plan to keep it off. Lifestyle changes are key.
Good luck!