Well, this could be because you're water fasting (extreme detox is happening) all the while you're putting more toxins in your blood stream via smoking. There is no way you can get around the fact of detoxing while on a fast, water or otherwise. But the detox is much much more extreme on a water fast. So, in essence, the poisons from the smoking are magnified a thousand fold.
My suggestion would be to drink raw live veggie juices (See post to you in response to mine, below) and try to cut down on the smoking and rest!