Walking for exercise

Anyone have any good luck walking for exercise? It's really hot, even at 10 am so I'm only walking for about 30 minutes bc that's all my 4 year old can handle. I've cut out cokes, from a 32 oz from McDonald's a day. Im 170 and really needing to loose some baby weight. I can't really diet right now bc I'm BF and my baby is smaller so I'm having to eat a lot.