Most likely the bulimia. Severe changes in your lifestyle have the ability to affect your cycle. I would talk to a doctor about it anyway. Bulimia has severe side effects on your body and organs that aren't necessarily noticeable, not to mention the things that you will notice. Bulimics are prone to hair loss, tooth decay, poor skin. They get sick more often. In the long run, your organs will start shutting down. It is very dangerous and can be deadly if continued. Talk to a doctor and get a counselor.
Good Luck.