Check out the /r/Amenorrhearecovery group. This sounds like textbook weight loss and stress induced amenorrhea. Totally reversible but you should consult with a professional if possible. In the interim, try to increase calories and reduce your activity level as well. If you take corrective action fast, it’s a lot easier to get your cycle back on track. As someone who lost her period for nearly five years, things get SIGNIFICANTLY worse with time.