When you say you don't eat sugar are you referring to just the white stuff?
Carbs convert to sugar in your body so if your are having lots of carbs bread and processed foods, you will gain weight.
Processed food is designed to have you eating more. It's a science. At the end of the day when it comes with freeloaders such as ill-health, it's not the cheap food it's purported to be.
You're right about genetics playing a role, but it is not always true .
If you want to regain your health and ditch your weight. have a look at Diet Doctor.com
There is some really helpful information on the sight, as well as stories of people who have turned their health around in amazing ways.
I have spent time in quite a few Asian countries and find it distressing that cultures that once enjoyed supreme health and slender bodies, now have a sizeable number of people hugely overweight.