Ag,
The third day blows--the third week is the worst!!!!! and you will have at least a couple funks in the third month. There is something about the 3's. That seems to be the trend for most quitters.
On my 15th or 16th day, I was sitting at my desk and had what can only be described as a fucking panic attack because of a major, major crave. It was so bad I got up and went home at 1pm.
It is all psychological, but remember, the brain is craving and giving you real physical sensations--mental craves give real physical sensations that feel as real as the first 4 days as the triggers pop up------Nervousness in your stomach---fatigue, anxiety etc. The good news is you only have to go through the third week once.
Be easy on yourself and you will make it through. The Craves will weaken with time---sometimes it is two steps back one step forward, but trust me they will weaken.
LL