I have sympathy. I've battled with my weight since I was 17 and don't get me wrong some people's composition makes them more vulnerable to putting on weight.
There's many reasons why I got fat, mostly due to my mental health and the way I treated my body during that time. But being fat itself was not an illness, I got fat because I regularly overdid food and booze without exercising. And I lost weight because I did the opposite over a sustained period.