Keep at it and stay strong. One tiny hint if it may help: Aside from the body being addicted to the chemical and hence withdrawal symptoms - there is a psychological aspect that can curb the crave. When you feel a real crave for a cigarette (or whatever) just remember that the crave will not last until you smoke (this is the trap). It lasts between 5-10 mins. So keeping this in mind you can actually outlast it more easily :)