3 years of amenorrhea certainly is not normal and I do think that you should have this situation checked out. So I recommend scheduling an appointment with an OBGYN. Not having your period per se is not dangerous, but the causes of your amenorrhea may need to be looked into. There are many causes of secondary amenorrhea (losing your period after having it at one time). The most common cause is pregnancy, but 3 years of not having your period is not likely to be due to pregnancy. The second most common cause in people your age is metabolic which is similar to why you probably lost your period when you and the eating disorder
as a teenager. I am concerned that your low calorie diet or low weight may be causing this phenomenon. If it has, then I am concerned that your at an unhealthy weight. The other possibility is that you have premature ovarian failure. Again, I would suggest that you schedule an appointment with an OBGYN. He or she will probably order some blood work to look for signs of premature menopause versus pituitary failure. Pituitary failure is what you would expect when someone is severely underweight. Primary pituitary problems such as a pituitary tumor are also problems that should be ruled out.