gas
What you're feeling is gas. You're taking GasX, but are you on a PPI, like Prilosec OTC once a day? GasX alone may not be enough (it wasn't for me). I still take Prilosec once a day at 7+ months out or I get terrible gas.
You just had all the nerves in your stomach cut, and you won't be feeling any actual fullness from food until you start eating solid proteins. Some people take months longer than that to feel actual fullness. This is why weighing and measuring your food is so terribly important. While in healing phase, and since you can't feel anything, many are tempted to eat more than they are told to, and risk doing serious damage to their new tummies.
While you are on liquids, purees, and soft foods, they slide right through your stomach. This gives your staple line a chance to heal without any pressure on it. When you do start eating solid proteins, be strict about how much you consume. NEVER guess, always measure during soft and for liquids, then weigh solids, and track every morsel.
Believe me, it's worth the trouble! Congrats on making it to the Loser's Bench!