Hi C.,
First kudos to you for still breastfeeding!!! I nursed my last baby for 18 months and hope to do the same with this one. From what I have heard, many people keep an extra 10-15 lbs while nursing. This is to keep your body supplied with the nutrients you need to sustain lactation. I think it all depends on someones body, maybe no matter how much you exercise, eat, etc. you will keep on those extra lbs. Just remind yourself that you are doing for the health of your sweet baby! ALso think about the type of exercise you are doing, mostly cardiovascular (kickboxing, step, running, etc) will help with weight loss. Any thing that has to do with weight-lifting will actually just build muscle reather than burn fat. That is another point, you are probably getting some strong biceps from holding your baby and muscle weights more than fat so that could be some of the extra weight, as well as the weight of bigger breasts. The types of food you eat will also make a difference. Of course fruit and veggies and some protein (don't forget calcium) are the best things. Try to avoid fried, processed, and high sugar foods. You probably already know this but your baby needs you to eat enough calories so that she (?) can get what she needs. This isn't a time to diet!
Anyway, I hope this is helpful. I apologize if you already knew all of this! Best of luck! -A.