Well...there IS 100% truth in the fact that your body burns a lot more calories than normal breastfeeding. (I am currently nursing my third child.) I think where people think it is a myth, is because women expect the weight to just fall off simply because they are nursing-this is definitely NOT so. Nursing burns between 400-700 calories a day making milk-depending on how much you are making/how much your child eats.
Just for estimations sake-we will say 500-600 calories. What is that? It can be a grande decaf mocha and an extra serving of vegetables at dinner...it can be a big slice of cake. It can be 2 slices of pizza. If you are eating high caloric foods-it isn't all that much. What I mean is-if you are eating more than your body is burning-including what it is burning through breastfeeding-you are still ging to gain/not lose weight. Calories in vs/ calories out.
You still have to watch what you eat if you want to lose-but if you are nursing, you can eat more calories per day AND LOSE than you would if you were not nursing-but a limited amount. Breastfeeding does not mean mindless eating and still losing weight.
I am currently losing eating around 2000 calories a day (meaning about 1500 for me...and 500 for the baby approximately give or take...) whereas I would be on about 1500-1600 a day right now if I were not nursing.
I understand your frustrations-but let me tell you something.
This is my third baby-and taking off the weight takes work, and it takes time. Also-your body will NEVER be exactly like it was before you had your first child. It just won't. Some women will have stretch marks, some wider hips, some will stay 5-10 pounds heavier than they did before they ever had kids...some will have permanently larger or smaller breasts than they did pre-pregnancy. There are changes when you become a mother.
You have to eat if you want to lose weight-but you have to eat a reduced calorie diet. Eat less than your body burns. Also, you HAVE to exercise. You nee to do cardio (walking, aerobics, etc.) to burn calories and help you to shed pounds. You are also going to have to do some strength work a couple times a week as well on your core muscles (abdominals and back) because they get compromised during pregnancy. Start strength training (a routine or video that includes ab and back exercises) or start doing Pilates which hits both of those areas. You have to regain the strength in your abs and back if you want your middle to regain its normal form. It isn't just about losing pounds...you have to get those muscles back into shape that were weakened during your pregnancy. It won't happen through diet alone. If you don't retrain those core muscles-you can lose pounds, but still have a weak back and the weakened, soft abs.