OH man. You need a hug. (((HUG)))
It's hard, but if you have been binging and purging for a while, and you are beginning to have health related problems, the best thing might be to tell someone. Is there anyone you can trust? A friend, a teacher, a counselor, your parents?
And also, purging is related to something emotional. Is there any commonality between your purgings? Maybe something happens and you feel scared/embarrassed/shy or something? Maybe while you're trying to decide whether to tell someone or not, you can try and see if you can pinpoint what might be the causes of your binging/purging.
I'm sorry if any of this sounds preachy. I didn't mean it to be.

I hope that you can get some help, some support from someone.

And one last (((HUG))).