Simply being overweight or obese is not a disability any more than being lazy is a disability. Then again, I am not saying that the obese are lazy, but it might be a cause of obesity. If there is an underlying medical condition that causes obesity, then that condition can be a disability. Obesity itself is not a disability, rather, it is simply a symptom of the underlying illness. Morbid obesity is disabling so I recommend you make a change before you get there.
I find myself in a tough situation when I am asked to fill out paperwork for handicap plates. I have had many patients ask for them for knee arthritis or pain. If I give them one, they will gain weight and the knee pain will be worse when they decide to walk. The food for thoughts here is simple. If you walked instead of riding the cart, you might not weight as much. If you gain weight, you knee pain will be worse. Think about it.
The bottom line: Handicap or disabled license plate and parking can do more harm and most conditions improve with some exercise.