Although her symptoms manifested themselves in a different fashion (mostly headaches), my mother had a TON of trouble shutting down her Pepsi habit. I see you've been a Pepsi drinker too, hehe, maybe they put something addictive in there
j/k
Seriously, I totally agree with hugmequick. Depending on how sensitive you are to caffeine, cutting it out of your diet can cause a lot of different withdrawal symptoms. National Geographic magazine recently ran an interesting article about caffeine. They showed MRI images of brain activity in individuals who usually consumed caffeine and were not allowed their cups of java--it wasn't pretty! Your body begins to rely on the stimulation and I think it's reasonable to expect some withdrawl symptoms.
Hang in there and give it some time... hopefully the pains and lethargy will clear up. Best of luck!
<--- a fine example of caffeine overload