Struggles with craving - its beginning again!

Well, here I am again. My brain is running out of artificially induced serotonin, the "feel good" neurotransmitter so I find myself wanting...something, anything that will give me another shot of that substance.
When this weekend arrives I will have been clean of marijuana and nicotine for three weeks - now that's the longest I have been without either of those intoxicants for the past two years or more! The marijuana has been easy by virtue of the fact I have removed myself from the environment in which I was in where everybody around me (even the neighbours) were regular smokers. I think that is the single biggest deciding factor. I mean it's not that I haven't wanted to stop for a long time; its just that my attempts have all been pretty half-hearted knowing as I have that sooner or later I would be offered a smoke by someone and that I would not have the willpower to say "no". Now that I don't have that issue, and because there are no easily obtainable sources close by by new house, it is just so much easier to resist the urge.
With cigarettes, the change of environment has also helped immensely. Once again, there are no smokers around, therfore, I am not being constantly subjected to the idea of smoking (although Hollywood doesn't help us much on that front!). With all these factors falling into place getting to this point has been about environment more than willpower. I think that the most important lesson I have learned in my journey through addiction is that we really don't have any willpower; rather, it's all about setting up a situation where temptation is removed and there ceases to be any need for willpower. However, now I am at this point and the chemicals are really clearing from my system, my brain is noticing this lack of pleasure-giving serotonin and sending the message that to remedy the situation I should seek out a cigarette and a joint. I just have to keep telling my brain that I am doing this for its own good, and that it will thank me further down the line. Once my body and brain reach a state approximating homeostasis then things will be a hell of a lot better for both my body and my brain. For now I just have to keep reminding myself of that fact and stick with the nicotine patches and lots of long walks to keep myself away from temptation.

I sure would appreciate any advice people have to offer...