I need to lose a huge amount, just under double what you need and it does seem daunting if you look at the whole picture...that's why I'm focusing on my "mini goal" of 5 stone...I'm nearly at 2 stone already after 6 weeks, so 5 stone doesn't seem that unachievable. Once I've completed the first goal, I'll start again with the second.
So you've got 8 stone to lose...why not set mini goals of say 2 stone each. Focus on getting to the first 2, notice and note down the changes after losing 2 stone and then move on to the next.
I wanted my first 5 stone off by mid June, so I've got nearly 4 months to do the rest, it feels good to be "on target"...so try setting yourself small goals and you'll feel good when you achieve them, which will hopefully spur you on.