I've pcos, fbs was 56mg/dl.my weight loss range is slow200-300g/week& rapid gain ability.do i need metformin&if so, should i've to use it for life long?

You shouldn't take: You may use metformin to control and regulates your blood glucose and lose weight.It should not be used life long, if you lose weight , your sugar will be normalized besides you get treatment plan with your ob/gyn doctor.

Possibly: Metformin can be useful for pcos but it is important to try to work on the underlying Insulin resistance in other ways as well. With your hypoglycemia you are probably pumping out a lot of Insulin and that is usually a result of a high carb diet. Lower your carbs, exercise and treat underlying vitamin deficiencies like B12 & d. Then consider metformin. Wouldn't make any lifelong decisions yet.