Habit is habit (Mark Twain)

Mark Twain wrote in Pudd'nhead Wilson, "Habit is habit, and not to be flung out of the window by any man, but coaxed downstairs a step at a time."
I am trying to stop my habit of drinking Diet Coke.  I'm not sure if it is an habit or an addiction, but either way; it has gotten totally out of control.  I don't like calling this effort a new years resolution but I guess I am under the influence of the season. It is just something I should do. That reminds me of another quote that I have had on my whiteboard for a number of years. "...Do what needs to be done, when it needs to be done, and do it with a cheerful heart." -Marjorie Hinckley.  That cheerful heart part is a real sticking point for me!
Today is day two of no Diet Coke which really translates into day two of no caffeine. I feel sluggish and lacking in motivation. I am trying very hard not to substitute sugar for caffeine. I wonder which is worse? I am hoping that taking vitamin B, iron, and fish oil will help me have more energy after a couple more days...oh, and aspirin for the inevitable headache (I have been down this road before without success so I know the drill)  Healthy habits and having fun have never been on the same page for me.  As always, I'm working on that cheerful heart thing.