Many people say that they have gas, constipation, and stomach pain after they quit smoking. Nicotine tells your digestive tract to move more quickly, which your body adjusts to over time when you start smoking. When you quit smoking, your digestive system can be thrown out of whack again for a couple of weeks by slowing down, causing discomfort. This is temporary and will go away as your gut readjusts to not having nicotine.
Medical review: Nathan Cobb, MD, November 6, 2017