Hello,,, weight gain in pcos is mainly due to hormonal imbalance, so it is pretty challenge to reduce weight but not impossible. Eat a high-fiber, low-sugar diet. Avoid processed and fatty foods .Eat four to six small meals throughout the day, rather than three large meals. This will help control your blood sugar levels.Exercise for at least 30 minutes a day. medications like metformin will help along with above diet, chart your weight to see prognosis, for further information on diet, can consult dietitian.