Hi, A.. I know it is tempting to try to go the fastest route to weight loss. The only true way to lose the weight and keep it off is lifestyle change - healthy eating combined with regular exercise. And not only will you lose your 15 lbs but you will be a role model of health to you child and hopefully live a more active and long life together with your family.
I recommend a fitness program that you do not do alone. Group support is amazing and makes it more FUN! If it is fun you are more likely to stick with it. My passion is Stroller Strides so you can work out with moms and keep your baby with you. www.strollerstrides.net/charleston (Disclosure - I am the owner of the Charleston program but I started out as new mom with 20 lbs to lose. Joined the program. Loved it. Ended up buying it and becoming passionate about health and fitness!) If you prefer a gym, join with a friend so you can help support each other. If you want a free choice, walk outside in your neighborhood. Just dont do it alone. You will find excuses not to go. Get a friend and keep each other accountable. Set a weekly schedule and follow it! It is always more fun with 2 or more and you are more likely to stick with it! YOU CAN DO IT!
Someone else recommended you journal your food at FitDay.com. That site is great and FREE.
Weight Watchers is a great program b/c it teaches you healthy nutrition choices and portion control and is not a diet that you do to lose weight and then are done with. It is a lifestyle change. LEAN Mommy, a book by Lisa Druxman, is also about lifestyle change and it helps you figure out the why's behind when and what you eat so you can start to change your mindset around eating (ie eating for comfort or out of loneliness, etc).
I do not know how much you weigh, only that you want to lose 15 lbs. If 15 will take you to your healthy or ideal weight then truthfully the last pounds are tough and take time. Might not be realistic by May in a healthy way. If you are very overweight and want to lost 15 to feel better that can be done a little faster. Ever watch the Biggest Loser? Great show! They are very overweight and can lose big pounds each week. It is not so fast with women who are not obese but just want to slim down. I just want you to be sure you are realistic about your timeframe for losing weight. You dont want to get disappointed if it doesnt fly off 10 lbs in one week, you know? For example, to lose my extra 20 lbs after my son was born I started working out in Jan (he was 3 months old) and was down to my size and weight goal by September. So 9 months to lose 20 pounds. Be sure to set realistic goals and know that YOU CAN DO IT!
So get a buddy. Set your fitness goals TOGETHER. Work on portion control and healthy choices (dont even let the junk in the house). YOU CAN DO IT!