Hi Meilyne!
I think you would feel best going after your ideal solution. I asked you for numbers because I wanted to see if there was any precedent for losing that much. I found this story online of a man who lost that much, here's the site (sorry I don't know how to link)
http://www.jewishworldreview.com/0104/300lbs.asp . I think a good way to do it would be to get a coach. Have you ever thought about this before? Every single being on this earth knows the difference between knowing what you should do and actually doing it yourself. Myself included! (I'm addicted to eating ice, which is bad for you to do). Anyways, if you could get a tough personal trainer, or even go on a show like "the biggest loser" or something, that may provide the structure you need to break the habit.
Here's wishing you luck!