My father died of emphysema, the last four months of his life were on a ventilator. He was conscious but couldn't eat, speak, leave the bed and knew the only way he was getting off the ventilator was by dying.
Nevertheless, I took up smoking at 17, too, and took to it like a duck to water. I always smoked upwards of a pack and a half a day. At the ten year mark I quit due to being hospitalized for a week with double pneumonia and managed to stay off them for several years. Since then I've been on and off several times, usually going back due to severe life stressors.
The cravings hit at odd times, the three day mark, the one week mark, the two week mark, etc. Seems to last for up to three months. You just have to drink a lot of water, breath through it, be patient with yourself and give yourself healthy rewards.
This information, though, in particular, has really helped me:
http://whyquit.com/whyquit/A_Benefits_Time_Table.html