Please help... I want to lose weight really bad. I just started?

back walking and eating healthy. I'm really big chested (40 DDD). My back hurts really bad due to this. That's my reason for not doing much exercise. It even hurts when I walk for more than 5 mins. Should I have a reduction before trying to lose weight? I don't want to look funny... like my stomach being bigger than my . Any suggestions?