S.K.
I am not saying anyone is wrong here but Grace did say realistic ideas and for breastfeeding mothers with 4 month olds simply want to nap still between bouts of baby being attached to your boob.
I started right after I had my daughter a year ago simply watching closely the number of calories I took in. I used a program called Weight-By-Date (available online at http://www.weightbydate.com/pro_overview.htm) and it takes about 15 minutes total of your time each day to put in what you ate. Use the calculators in the program to determine you ideal calorie intake (for instance, mine is 1700 calories) and try to stay 200 calories under that. Eat whatever you want, just be mindful of the calories.
I have lost 50lbs in the past year with this method. I am a couch potato, I take my daughter out on walks now and then but I by no means exercize any mroe then my daughter makes me. I did a yoga-pilates tape for a while to help stretch and repair all of the muscles in my body (if you have nexflix get Crunch: Super Slimdown Pilates Yoga Blend) and it helped bring the loose skin back into order. It's very low-impant and takes about 30 minutes to do. That's it.
Between those two things, I've lost my pregnancy weight plus 30lbs (totaling 50lbs) and I'm losing about 2 lbs a week. Keep in mind, 2lbs a week is healthy weight loss. Anything mroe then that is being a bit too agressive and you're more likely to put it back on, and TWICE as much as you lost!
Patience and perserverence.