All babies get gassy tummies! in order to grow, babies take in 100 kcal for each kilogram they weigh! this is a lot of hard work on their digestive system. (imagine digesting 7000 calories per day.
.......You would be gassy too!) babies have immature gastrointestinal tracts too. Digestion, and gassiness, often get much better between 4-6 weeks of age.