I read your post and it reminded me so much of myself when I was your age. Like you, my problem began when I was 17 years old. I am now 37!! I started out as an anorexic and became bulimic as a result of counseling. The counselors think the right thing to say is "all you have to do is eat, and you can go home" wrong!! What they taught me is how to eat, make everyone else happy, then puke my guts up!!
After 20 years of this, I still struggle on an almost daily basis. I have found out that there is definitely a root problem that causes us to think that we are not good enough or don't look good enough, so we have to do this terrible thing to ourselves. When I was about 27 years old, the realization of what my "root"problem is came to me (yeah, 10 years later). What I realized was that at a very crucial point in my life, I felt like I was not being the person my father expected me to be, and at the same time, I had a boyfriend absolutely break my heart! In some twisted way, I made myself out to be the bad guy because if I was skinnier, or could control myself better, these things would not have happened. ( I was 5 ft 9 in and weighed 117 lbs for god's sake!!) it was a yo-yo affect-if I couldn't satisfy a male person in my life--regardless of what their role in my life was- boyfriend, dad, boss, husband- I thought that if I had the perfect body--these things wouldn't have happened - afterall--everyone likes the pretty, skinny girl, right?
Don't get me wrong--i'm still not 100% well. But I am able to catch myself and try to control it from happening. It has been a very long, uphill battle. I see the affects it has had on my body for the past 20 years--deteriorating teeth, having callouses frozen off my fingers, no periods for over a year--risking not being able to have my 2 beautiful children, thin hair, terrible skin texture. I have even been through having to take immodium before I eat because after I would eat, in trying to mentally talk myself out of sticking my finger down my throat, I would get diarrhea so bad that it was almost uncontrollable, and pieces of food would actually come out!! I know this sounds terribly gross-but it is the reality.
Counseling doesn't work for everyone. Take a good look inside yourself and those that you surround yourself with. If someone is constantly saying something negative to you ro making you feel terrible about yourself, your best therapy may be to exclude them from your life. It may hurt--but it hurts you a lot less than you'll hurt yourself.
I wish you luck!