It took me a month of living with withdrawal symptoms and headaches to get over the addiction.
Let me just point out that this is totally not normal. I drink 10-15 (20-oz) cups of coffee a week, in addition to caffeinated sodas, and when I'd go off caffeine for a few weeks (as I used to do regularly), I'd have 2-3 days of feeling depressed from normal, and a very mild but persistent headache over the first 1-2 days of it. If someone has caffeine withdrawal symptoms for a month, I'd think something else is wrong.