I haven't gotten my period for a couple months. i can't be pregnant, but i am on a diet called ideal protein. what could cause this ?

Hormone imbalance: It is possible the change in diet is affecting the hormones and resulting in no periods. Be sure to eat a healthy diet with fresh vegetables, fruits, and healthy meats and essential fatty acids. If your weight is normal and you are getting a good night sleep, and moving through the day and managing stress well your periods are likely to return.