Hey! I'm new here, but I wanted to comment as I've had your same exact observation in the past about vaping. Actually, the fact that you gain weight is actually to be expected considering that VG while being sugar free, will actually cause you to have a spike in insulin due to the carbohydrates. VG is "sugar free", but carbs in it and in high enough quantity (VG has 5 grams per teaspoon which is considerable because of how much of that goes into our blood stream through the lungs) will most definitely affect blood sugar. This in turn causes insulin to go to work and the insulin then clears the complex carbs out of your blood and stores it as fat. By giving yourself a steady stream of carbs, your body will not burn fat because it's too busy trying to normalize blood sugar.
Check this out: just as an experiment, go back to another nicotine source like a patch or smoking etc for a short period of time if you have to and then cut sugar and carbs completely out of your diet for an entire week, or even just 3 days, and watch yourself lose weight. Guarantee you will lose weight (and water weight too because carbs and sugar cause water retention). If you eat fatty meats, fish, vegetables, butter, cream, and then cut carbs and sugar completely out of your diet with zero tolerance then you will drop weight faster than anything else you've ever seen. The experiment would just serve to prove that the increased complex sugars introduced by the VG is in fact causing the weight gain. The VG in the vape juice is keeping people in a constant state of sugar storage. Also, VG causes a huge increase in triglycerides. Not good
Sorry for the long reply but I couldn't help but respond. I've been studying medicine and nutrition for years, so I know a lot about the topic. Also, if you're curious, I quit vaping a few months after I started a couple years ago because it caused me to gain weight as well. Just my 2 cents and I hope that brings some perspective to the table.