PCOS can intensify insulin resistance, androgen-related symptoms, sleep problems, psychological burden, and weight stigma. It can make weight management harder, but PCOS is not defined by obesity and weight loss is not the only treatment.
Overt hypothyroidism can cause weight gain, but the typical effect is often modest and partly due to salt and water retention. It does not explain every case of obesity.
Pathological cortisol excess can cause central fat accumulation and severe metabolic disease. Ordinary psychological stress may influence appetite and sleep, but a single random cortisol value cannot diagnose the cause of belly fat.
Leptin resistance is an important model of why high fat stores do not automatically suppress appetite in common obesity, but it is not a routine laboratory diagnosis with a simple supplement cure.
Women do not universally lose less weight than men, but sex-related body composition, reproductive hormones, pregnancy, menopause, social roles, and treatment access can create different trajectories.