I understand your feeling.
It will b very hard to to maintain shape and weight with pcod. It is because of the hormonal imbalanace thode which are reason for your menstrual periods. Because of the imbalance there will be weight gain. If you are already on treatment then continue your treatment and along with the start doing the physical activity. If you can swim then it would he the best choice to burn your calories and also with that you need to maintain your diet. But diet not starving it is just remodeling your intake of food.