Ok I am just going to say it- this might sound like lame advice in the end but hope it doesn't-
I am having the same problem but for a differnt reason (I have severe allergies that casue me to have asthma like attacks and I end up on a breathing machine for weeks sometimes).
So, what have I done? Well, to be honest, it has made me crazy at times. Especially if like you say, the stress in my life has been through the roof, and I am dealing with urges to SI.
Everyone is different on this and that is why I said my advice might sound lame, but here goes:
Find something to replace the smoking habit, something that lets your hands and mind keep busy is the best, but if nothing else keeping your hands occupied is a good first step. Sugar-free lollypops, writing in a journal, exercise, playing with a toothpick....
Also some say just anything distracting...even playing online games or using distractions here.
Then of course there are the ways to get your "fix" without hurting your lungs with things like nicotene gum, patches, etc if you just have to have it for a while but CANNOT smoke.
I am having a very hard time too just like you so you aren't alone. I am using a bunch of differnt things depending on the day and my mood.
Good luck with it. I know you can get through it, but I also know how hard it is! Please don't be too hard on yourself if you do slip up.