going to the doctor is always the right option if the condition is intense or prolonged, but I've also had some tummy discomfort at times, since i started vaping 3 months ago.
initially i thought it was a reaction to pg or vg, but I've now narrowed it to 3 factors. each person is different and vaping is not a consistent activity. things change from coil to coil and juice to juice and person to person. factors like stress and fiber intake and health conditions, can be the cause, but, as for vaping:
1) water. we simply don't get enough water. i didn't get enough water before vaping and i sure don't get enough now. dehydration can affect the output or your tummy (google it).
2) nicotine. amount of nicotine can vary wildly with coil setup, device, juice. too much nicotine will affect the output of your tummy (google it). vaping, specially until you find your stride, can involve large swings on nicotine intake.
3) flavors. some flavors immediately have an effect on me. normally the overly sweet or fancy dessert flavors. i've narrowed it to the artificial sweeteners, and some juices do have them, and to fancy sweet complex flavors. interestingly i never had this from the top notch juice producers, ahlusion, 5 pawns, etc. same as smokers, a percentage of the vapor does take a detour and goes to the stomach instead of the lungs.
some people are more sensitive to this than other, thus not a problem to the majority, and it is hard to find a discussion on this issue here (or anywhere). the above is my experience. one of the reasons i feel that vaping and juices production could use a bit more scrutiny (without the current FDA witch hunt approach).
since I increased the water intake, reduced the nicotine rate, and took to (using just a few) simple juices from top vendors, I've been problem free. except for stress. gotta find me a palliative for the wife/kids/taxes/work conundrum.