I pretty much have the same problem. I started smoking cigs at around 14ish. I started smoking pot about a year later. Then before I knew it I was doing coke, xanax, alchohol, and even dramamine. I smoked laced joints pretty much on a daily basis for a long time. I'm 23 now and about 3 years ago I dropped everything (besides cigs) as if it never even existed. But I can't quit smoking to save my life. About a month ago I started taking it more seriously. But the longest I've lasted so far is about 3 hours. :\