As per my knowledge gas during pregnancy is because of changes in hormones which slows down digestion and increases gas. In later stages growing uterus narrows the abdominal area and thus pushes your stomach making you feel gassy all the time. Follow few tips to ease the situation
Eat less food with fewer intervals.
Avoid talking while having food, so that you absorb less ai
Don't drink water during meals. Drink 10 mins before or after having meals.
Check here for more tips http://www.momjunction.com/articles/remedies-bloating-pregnancy_0075362/