Sorry,
I'm 26 years old male. I have few extra pounds, but i'm not fat. My legs have always been more fat than the rest of my body.
You don't say whether you are a man or woman. Women can get vaginal/genital odors that can be a sign of infection, especially with bacterial vaginosis or trichomonas. No STD causes actual skin odor. Often it's a sign of bacterial overgrowth, which is expecially common in overweight people. I don't know of any solution other than what you're already doing--wash often, loose-fitting underwear, etc.
HHH, MD