I highly doubt that you get more nic with analogs. In fact, when I began vaping (18mg, then 12mg), I OD'd a couple of times (no headaches or anything, I just got very cold and a feeling like my skin would "shrink"). Definitely the vasoconstricting effect of nicotine (and I smoked 20-40 self-rolled per day, with pretty strong tobacco before, without ever feeling OD'd). Vaping with just nicotine is just pretty different from all the stuff you're getting with tobacco smoke and you end up consuming huge quantities of nicotine, but the tolerance builds up very fast anyway. I think, if you feel sick after smoking an analog after a big pause, you just feel "poisoned", since your body "forgets" how to deal with all the other stuff in the smoke.
I definitely want to try WTA liquid, maybe then I won't feel the need to smoke as well.