I was one of the select few who actually gained while BFing. It was totally my fault, I was eating the wrong foods. Once I realised that hey I CAN BF without eating a couple of pieces of cheesecake a day was a big moment for me.
I did Weight Watchers (they have a programme for nursing mums) and lost 13kg. I gained about 4 back over summer while travelling so I'm back on the diet.
I didn't really do any extra exercise (just my normal walking to and from work, chasing after my kid, walking to the shops etc) but limited my junk intake and the weight came off. It wasn't that hard, I don't know why I took so long to get started...
I envy anyone who can say it wasn't that hard to lose weight. Right now I eat an extremely restricted diet, exercise and am really active--walking all day, every day and on my feet and of course the mommy stuff of chasing after an active kid and I still have that darn 15 kg to lose! But, with the weight watchers thing, I'm totally anti-synthetic sweeteners because of how harmful they can be to the body so I don't think I would be up for WW.