I switched from analog clove cigarettes to vaping in late October, and I have put on about 7 lbs. I didn't even think about the possibility of its being due to quitting smoking until I read this thread, though! I just sort of assumed that, since I was still getting the stimulant nicotine, it wouldn't be an issue. I think that, for me, the reason I've been gaining is that, since I switched to vapor, I spend a lot more time by myself, indoors. Regaining my sense of smell (during the first week!) makes it annoying for me to be around smokers, because it smells so awful and I'm now ultra-paranoid about the smell getting in my hair. Unfortunately, being a smoker for 15 years meant that a lot of my social relationships were based on finding other people to smoke with.
On previous quit attempts, I've noticed that I've gotten depressed when I quit, as if I had lost a friend. Although that's much less significant this time around, I have noticed it a bit, and I guess that might also be keeping me solitary and indoors.
I figure that I just need to keep hitting the gym, enjoying my newfound lung capacity (anyone else noticed this?), and getting tremendous jollies out of vaping in the locker room as soon as I'm done with my workouts. New habits take awhile to form, so I guess it's just a question of adjusting to the new lifestyle over time.