Thank you for asking such a fascinating question.
What you describe is called the delayed sleep phase syndrome, a form of sleep disorder that involves the circadian rhythm or body clock.
Most people sleep at 11-12 midnight and then wake up at 5-7 am. You sleep late and wake up late, and that is what delayed sleep phase means. In terms of hours of sleep, 6 hours sound fairly decent for an adult but for a teenager it may not be enough. The important question would be whether you feel refreshed or rested when you wake up naturally.
In order to retrain the biological clock and re-establish your circadian rhythm, what you can do is to get exposure to sunlight in the morning like 7 am or so. You can, for instance, take a walk in the park for half an hour or so. There is no need to stare at the sun as that will cause harm to your eyes. The sunlight will indicate to your brain that it is already daytime and that you need to stay awake and be alert. Exposure to light in the morning will help to bring forward the surge of melatonin (which the brain normally produces when exposed to darkness) at night and that will enable you to fall asleep at an earlier time of the night.
Your doctor may also recommend the use of bright light therapy from an artificial source like a light box.
Having odd hours of sleep may create stress for the individual as her work life, family life and ability to attend school or university may be adversely affected. Very often, the parents would nag at them and keep reminding them to sleep early and wake up early. Constant nagging and incessant reminders can also generate a lot of stress for the individual. Stress, anxiety and depression are known to affect menstrual cycle in that the periods may become irregular, last fewer days, or even last more days.
For treatment of your sleep problems, you may consider seeking treatment from a psychiatrist who has interest in sleep disorders.
Cheers! Take good care of your sleeping pattern. If we take good care of our sleep, many things in life will fall in place.
