Oooooh, I am SO THERE. I am cutting out caffeine right now and it is so hard! I drank easily three diet cokes per day. Not the cans, the big 32/44 oz cups. Yuck.
My body ached, and was always craving sweets and the headaches were awful on the days that I went without.
Hunker down and do your best, but allow yourself a treat at least once or twice a week. But my advice is to start drinking water, water, water. As much as you can stand and it will help get it all out of your system. (At least that is what worked for me.)
Good luck, this isn't easy, but I have to admit, I sleep better, eat less sweets and amazingly (shock!!) I have saved a TON of money!! :)
Keep us posted!