Hi Jeff, the constant thoughts of smoking in the early days of quitting is completely normal and one of the most frustrating parts of quitting for many of us. I believe its the cause of a few people losing their quits just to get relief from it. The problem with that is, as you've seen over and over, you have to begin at step one all over again when you decide to "stop" again.
The constant thoughts won't last forever but you will need to go through them to get past them.
Its obvious you want to quit because you keep trying. So my suggestion is to use the clues given to you to help. My air cigarette and soft peppermint puffs helped me through my whole first year. I also would remind myself over and over again the reasons for my quitting. I would tell myself things like "all good(?) things must come to an end". And then compare it to things I outgrew or got too old to do anymore like dirt bike riding or amusement park rides. Those types of things. Also remember that you're choosing to quit. You can smoke anytime you want, you just don't want to anymore. Those are the things that helped me.
Keep your goal of 18 weeks because I REALLY think by then you'll start feeling better. And lean on us to help get you there