I nursed my oldest for 38 months and my 18 month old is still nursing. My body hangs onto about 10lbs while nursing, and I can't seem to do anything to convince it otherwise. But, I have been trying to loose just by counting calories for the past 18 months, with no measurable success. I started working out in February and I am finally seeing some loss. I have only lost 9lbs since Jan 28, but I have lost 11.25 inches since Feb 5.
I know the last 10 pounds will stick around until she weans, but I figure exercise is speeding up my metabolism and making me stronger and healthier, so that 10lbs will come off faster when the time comes.
Because my daughter is 18 months and I am no longer her primary source of calories and nutrition, I only allot 200 extra calories a day for nursing. I can't post links yet, but I was just reading on Kellymom this week about how to determine how many calories to allot depending on the age of your child. It's all just a rule of thumb, of course, and there are exceptions, but it was a good read.