This is primarily caused by whole tobacco alkaloid withdrawal. lotsoffish is correct, WTA liquid will probably help you kick that last cigarette. The other option, and my personally preference, is to just vape your face off and break that alkaloid addiction. The withdrawal symptoms are pretty minor compared nicotine withdrawal but take seem to take longer to break.
That said, there isn't any real problem with using WTA liquid all the time if that's what it takes for someone to quit smoking, you just miss out on one of the, in my humble opinion, best things about vaping. Basically, with out those alkaloids, nicotine isn't nearly as addictive. I vape nicotine regularly, as a personal choice, but I can set my Provari down for an entire day if I get busy and be fine. No way I could do that when I was smoking, the addiction made itself known and demanded satisfaction. Now a days, there's a whole lot less pressure, and nicotine is just something that I enjoy for its effects, much like caffeine.
So, TL DR version, try some WTA juice, and then try to longer and longer between using it until you can put it down forever, I think you'll be glad you did even if your goal isn't total nicotine cessation. If quitting nicotine and eventually vaping is your long term goal, then breaking that WTA addiction will help you even more.