Dinky, I had similar problems as you do. I quit for about 6 months using the e-cig (relapsed terribly for the usual reasons), but during that time I had long coma-like naps, combined with virtually no energy, and an inability to sleep at night. Plus, my tendency to have itchy skin got much, much worse. I hesitate to offer any advice, given your medical history, but I figure this may help give you a different way of looking at it.
My pet theory is that when you quit smoking, there are many things going on. You are healing, you are purging yourself of some pretty nasty chemicals, and both your body and mind have become totally dependent on cigs, for a wide variety of reasons. This combination, while healthy, is also very stressful. It took me a long time of experimenting before I found the culprits.
I think that as your body goes through these changes, it becomes hyper-sensitive to things that either were there all the time, or were masked by the cigarettes themselves. I discovered three things.
First and foremost, I don't tolerate wheat (or other gluten bearing grains) very well at all. This never bothered me when smoking, but now it is pretty hard for me to ignore. If I eat wheat, I will be tired for the rest of the day, and will usually fall into a deep nap at some point. If I don't eat wheat, I will have a ridiculous amount of energy. I think this gluten intolerance got worse during my smoking years, but was masked by the self-medicating effects of cigarettes (I still eat wheat, but do so only occasionally, and when I know that I can afford to be tired).
Second, I have a similar, but less pronounced, problem with dairy. Milk and heavy cheeses in particular.
Third, my body craves low intensity exercise, such as walking. When I was smoking, I would lift weights and actually do a fair amount of medium intensity exercise, at least as much as my lungs could handle. But with
vaping, I need to walk and keep moving. BTW and FWIW, there are a lot of body builder/weight lifter type of trainers who think that low intensity exercise is far more important than medium intensity exercise.
Finally (I guess there were four things after all), my allergies got much worse. I cannot tolerate much in terms of mold or dust anymore. A HEPA air filter has helped enormously in this regard.
I hope you find your answers. And good luck.