Not medical advice, just some thoughts:
...snip....To think at the end of the summer I was down to 12Mg, and vapping 1/2 a ml a day......WTF happened? ... snip...
IMHO... that's what happened. You nailed it already. Too little nicotine, and back to the smokes! I don't suggest 48 mg, but hey that's me and not you. I do know the following from "quit smoking" classes and help sessions:
Your brain gets modified to want/need nicotine. The neurons change. And... it takes a long time, if ever, to lose [most of] that. Your brain... off nicotine... will adjust eventually. But, it's an addiction. Never anywhere else in your body. Your brian. Your neurons. And it's nice to say... "we'll I'm down to 12 mg now...." But it takes a loooong time to change for most people. And it never really goes away (the addiction). Once and addict, always an addict they say. It varies a bit based on the age you started, how much exposure you had, your specific biochemistry, depression, etc. The MAOI effect is powerful too. In fact, MAOIs are beneficial for some. So.......
I'd say try not to lower your nic too fast (don't OD either!!!). Snus may help. They are working on some "safer snus" too.... see the news section of the forum. Also, your doctor should discuss this stuff with you.
Don't feel bad for falling "off the wagon". Meh. Get back on. Just don't cut down so fast that you crave cigs over e-cigs. Your doctor may give you other options, esp for the MAOI issues if you feel that is a factor for you.
And a 5v mod may help out too! A box mod with 2 14500's + a charger. Not overly pricey to try it out. Also, a 5 v direct PT with 2.0 amp "wall wort" may work to try 5v.
Good Luck, don't feel bad, and have a happy new year!