I didn't experience nausea from withdrawal, but I think some people do. Sounds like your addiction is deep rooted and that's nothing to be afraid of. Keep doing what you're doing - weaning down. It will eventually get easier my friend, I promise that much
And do what Clark suggested, load up some 18mg and vape like a mad man when that craving hits. Worst case scenario the nausea won't subside so smoke a cig if need be. I would also recommend eating a little something when this hits, try to appease the nausea with some salty crackers or maybe even something with more substance if you feel like you can handle it. Maybe try a few crackers then vape and see if it does the trick.
I get nauseous when I vape too much nic on an empty stomach. I don't want to stop vaping so I eat something healthy and then vape again. Vaping has made me eat more food for this reason lol which is good I'm skin and bones

could also be appetite is coming back from not smoking for a month though.
A month ago, June 24th was my last cig...soon enough you'll be able to say that, too my friend. Just don't push too hard too fast. I had to wean off it too. Went to 3 a day, then eventually to one a day, then none. It's important to not push too hard though