On the ketogenic diet, carbohydrates are restricted and so cannot provide for all the metabolic needs of the body. Instead, fatty acids are used as the major source of fuel. These are used through fatty-acid oxidation in the cell's mitochondria (the energy-producing parts of the cell). Humans can convert some amino acids into glucose by a process called gluconeogenesis, but cannot do this by using fatty acids. Since amino acids are needed to make proteins, which are essential for growth and repair of body tissues, these cannot be used only to produce glucose. This could pose a problem for the brain, since it is normally fuelled solely by glucose, and most fatty acids do not cross the blood–brain barrier. However, the liver can use long-chain fatty acids to synthesise the three ketone bodies β-hydroxybutyrate, acetoacetate and acetone. These ketone bodies enter the brain and partially substitute for blood glucose as a source of energy.
If you start at 25g of net carbs a day, you can slowly increase to 50g as you lose weight. Once you reach your goal, you can increase your carbs as you see how they affect your weight. If you eat fruit for a week and gain weight, cut back. You have to figure out what works best for you. Ketosis can be maintained with as many as 100g of carbs each day.
I have PCOS as well. Research a PCOS-specific diet. It often overlaps with Keto or Paleo recipes. But you have to also avoid holstein cow produced dairy products, red meat, pork, soy products (which are in almost every processed food) in addition to carbs and sugar. And absolutely avoid anything you can’t be sure doesn’t have extra hormones injected into it (like many mass-farmed meats). Vigorous exercise is also necessary to lose weight when you have PCOS (It’s much, much more difficult for us to lose weight than people with normal hormonal balances).