I am a 22-year-old woman and am 5'6'. My weight is currently 68 kg. Am I overweight and should I lose some weight?
you have HIGH BMI. your weight is at marginally elevated level with respect to your gender, age and height. It should still be fine for your health but as per the standard definition: you are overweight.
With a good balance of body fat and muscle mass, your blood pressure, cholesterol and blood sugar values should still remain at more or less moderate levels. You would then be quite well protected against a heart attack, stroke or diabetes. This might be less so if your body fat is higher with a lower muscle mass, if you consume tobacco, other drugs or too much alcohol, lack physical activity or sleep, eat unhealthy food, or suffer from stress and other unhealthy life factors.
Further, at this weight level, you have marginal risk of gaining weight. If you don't have sufficient muscle mass, then its the right time for you to start exercising, eating healthy food and try to increase your metabolic rate. Eat a variety of foods that you like, optimally including five servings of fruit and/or vegetables a day. Avoid eating too sweet, too fat and too much. make sure to do physical exercise at least for half an hour daily at moderate to vigorous intensity.