After you heal its really persistant vomiting that makes the band slip. Sometimes the doctor gives the patients some anti-nausea meds to take at home just in case. Early vomiting is bad, but occasional vomiting doesn't usually dislodge the band.
The band doesn't get adjusted for 6 weeks. Sometimes the band is very loose when placed around the stomach. Patients are expected to lose weight because they are on a calorie restricted modified diet the first 6 weeks. If you are eating now, you can be creating serious issues.
Remember, surgery never fails, the patient does.