It could also be the way you're inhaling the vapor. You don't inhale it the same way you do a cigarette. With a cigarette it's a short, hard puff, deep inhale; with e-cigs, it's a long, slow, easy pull, then let it linger in mouth and throat for a bit before inhaling (or even instead of inhaling), then slowly exhale via nose, or nose and mouth. In vapor, the nicotine absorbs better in the soft tissues of mouth, throat, and nose, rather than in the lungs. With cigarette smoke, the combustion particles in the smoke are so fine, nicotine absorbs better in the lungs.
When I realized I was trying to vape the same way I smoked, but was still having to go out for that "first smoke of the day" (the only one I smoked, for the last 3 days I smoked), I started paying attention to inhaling more slowly with vapor, and that night, while practicing those long, slow inhales, I managed to get so much nicotine into myself, I got the sharp stomach pains -- and I was vaping 6mg. The next morning, instead of running right out to get that first smoke, I vaped, doing the long, slow inhales, nose exhales -- and that was my first smoke-free day.
Cigarette satisfaction is immediate; the satisfaction with vaping takes longer, 5-15 minutes. But if you can make yourself slow down and take your time, you get every bit as much satisfaction from vaping.
Andria
But after about 5-6 hits... I go back to strawberries and cream. 
