I don't think you're doing anything wrong, per se, but there are a couple of things you can take a look at that might help. One is the nicotine level you're currently using. You didn't specify this in your post, but say that right now you're using 18mg. That might not be enough for you, so bump it to 24mg and see if that takes the edge off of your cravings. If you're already using 24mg you can try 36mg, but I wouldn't go higher than that. You might also want to consider getting a larger battery, such as a Riva or an eGo because it sounds like you smoked A LOT! The regular 510 might not be enough for you.
You might also want to look at how attached you are to cigarettes. Yes, I said attached. It sounds like there might be a comfort level associated with them that you just aren't ready, or even willing, to leave right now. I don't want to sound terse or mean, so please don't take it that way, but you have some other issues going on. The thought of quitting analogs might be a little tough to handle and trying to do so all at once might not be a good idea.
There are plenty of people on this forum who are still smoking even though they also vape. There is absolutely NOTHING wrong with this. Everyone is different and sometimes making the switch immediately doesn't work. I would try not to focus on the cancer thing too much. Getting fixated isn't going to help you. Just ease into it and do what feels comfortable for you. There's no pressure here, really. Try the things I suggested and see if that might help, even if it just helps you smoke less.