I had a couple days where my stomach was so swelled up I looked pregnant! Really bad gas pains and gas. It reminded me of the one and ONLY time I made the mistake of eating too many sugar free candies! I don't think mine was because of withdrawal as I was still smoking a few cigs but it only last a few days and did get better thank goodness!
It actually can be from very subtle withdrawal if your nicotine intake was going down. Nicotine accelerates your digestive system (just like it accelerates your brain).
Until you re-adjust, that can lead to gas, constipation, swings between constipation and...well, the reverse, and so on.
Now that you mention this, I do remember the same during my transition period, and like you I didn't cut the cigs all at once. It went away pretty quickly.