hey kaleena
i did the same as you for a really long time and never told anyone about it either ... and was always pretty much of normal type weight ...
i don't really have much to say to help but ... i got rid of it by learning lots about food and exercise so i lost weight in a more sensible way and i think my metabolism is improving after so many years of f**king it aournd. your reasons for binge/purging may be completely different to mine ... i've only ever done it to control how i look (which in turn contributes to my self esteem .. etc etc).
I still have a problem with it when I put on weight for an uncontrollable reason - i have had some depression in the last year and while prozac made me sick and decreased my appetite, celexa made me crave food sooo badly.
funnily enough i have just finished my PhD in psychology.
sorry this is a bit of a ramble ... there are people in here who have some really good advice and insights, and i hope it helps you.