I have the same problem and my youngets is going to turn 2 soon. I feel I eat pretty healthily, etc. no major soda habit or anything like that.
I would suggest keeping a food diary, I started doing that on SparkPeople.com ( you cna add the foods and wuantities you eat every day and it will calculate your calories for you - it is free too) and realized how much those little sweet snacks are adding up, and measure everything you eat, at least while you keep the food diary for a week or so. It will give you a more realistic picture. I know I tend to keep eating like I did when pregnant, I think, and although nursing doesn burn extra calories, they decrease with the baby's age and decrease when baby starts eating solids, which yours peobably does, now. But we adults get in a habit/rut and keep doing the same things on auto pilot.
I am trying to downsize portions, and eat 5 times a day in very small portions, compared to 3 regular sized meals a day. It is hard, but I have lost 6 pounds in 2 weeks, from 180 to 174 and I am 5'2". I did lose a little while nursing, down to 160 ish, but it got harder, actually after I stopped nursing, I started gaining weight, and leveled off at where I was at the 8th month of both pregnancies. ;-( SO be prepared to have to cut out a decent amount of calories just to maintain weight when you stop nursing, and even more to drop weight - I also am in the blizzard bound North central IL, and we bought a treadmill, because though I feel I do alot of stairs and lifting with 2 toddlers, I am definitely not active enough. I am starting to walk the treadmill for 30 minutes every other day, and will work my way up to more, so I don't over do it and burn out and quit.
Good Luck,
It is along haul, but we need to get healthy for our kids!
Jessie
Good Luck....