Have you looked into Paul McKenna's book and Cd pack, 'I can make you thin'?
It sounds like you haven't yet got thin in your mind, in a way that you think of yourself as thin, so as soon as you take your watchful eye off your subconscious, it starts to crank the weight back up to where it's internal thermostat is set, if you see what I mean.
You could try 'Peak Performance', 'Break The Habit' and 'New Behaviour Generator' too.
