It could also be you are swallowing nicotine more. Most nicotine in vaping is absorbed in the mouth, nose and throat, and thus some can end up in the stomach. If you are finding that you are getting juice in the mouth a lot, this can happen more. Roly's suggestion about trying PG is good if you can tolerate PG. Personally I cannot tolerate PG and it itself will give me various gastric issues, including gas.
But yes, often in the beginning if you are seriously cutting back or quitting smokes entirely, there can be gastric issues, such as constipation, gas, and general discomfort.