Why would I lose my perriod at 21 years of age?

I have not had a period in about 2 years. Before that my periods were always regular until 2 months before it completely came to a halt. I eat extremely healthy and workout everyday. I also am at a healthy weight although I do stress a lot. I do not have insurance so I cannot go to the doctor. What could be the possibilities of this? I am a bit nervous.