The combination of your athletics and your anorexia is VERY dangerous. Do you run a car with no oil or gas in it? This is very serious and I would suggest you see your doctor (if you do not go to the ER) and she will request a full blood workup. You could be deprived of everything including important electrolytes, and this could cause all manner of complications including cardiac arrest. Do yourself and your body (that doesn't deserve this) a favor and see a doctor. You cannot continue to run on empty. Do you want children someday? Anorexia can impair or totally wipe out fertility. Also, if there's something brewing beneath the surface, don't get all squeamish about seeing a counselor- most people in this day and age will need to see one and it's actually kind of fun. Plus, you get to vent and hear an objective point of view to everything...no bias whatsoever. Please, take care of yourself now.
What should you do? If you ever think that there is anything wrong with you, you should always see a doctor.
And if you're still anorexic, you should definitely get help for that. Do you want to die?
If you are anorexic that will screw up your periods totally. Your body thinks it's going into famine mode (as indeed it is) and tries to make sure you could not conceive because you could not carry a child to term with no food.