My first thought here is adhesions. Abdominal pain is a key symptom, but bowel obstructions are the most serious side effects. So trapped gas and serious constipation wouldn't be surprising. Medical papers reference difficulty with adhesions to the band itself when they try and reverse the surgery. IDT there's any treatment with this kind of thing outside surgery, but any abdominal surgery runs the risk of creating adhesions itself. I would make sure your motility is not severely compromised. Slow motility can cause these symptoms too. If constipation is a major issue for you, I would start there. If it's not manageable by yourself, you should talk to your GI about some meds like Liness and Motegrity.