I'm on Day 85 and I'm pretty confident that the "theory of firsts" is the best I can explain. Basically, the first time you do or experience anything after you quit you'll experience cravings. For instance, last Friday afternoon I had huge cravings and it took me a minute to figure out why. I was at work, leaving our quarterly sales meeting when I realized that it was my first quarterly sales meeting since I quit. The end of the meeting was always a relief as there's a lot of work that goes into it, and I always reached for a cigarette first thing when it was over. I had to remind myself that I was feeling that way because of the mental trigger that says "end of meeting = cigarette", not because I actually wanted to ruin my quit and have a smoke. Overall, the psychological triggers stop coming after you overcome each new "first" without smoking. You'll continue to have firsts for a while, but just try to remember that as you encounter each craving. It's just habit, not desire.
Best of luck,