Suggest Treatment For Swollen Stomach

Whenever I eat lunch at my desk at work or when I am extremely stressed, I have episodes of vomiting with terrible upper abdominal pains that remain for a couple of days after the vomiting episodes have ended. I am very weak and cannot stand up straight from the pain. A couple of times, I have passed out while vomiting. I have seen my GI several times for various tests. He thinks it is IBS & has given me Symax Duotab to take if I feel an episode coming on. Also, my upper & lower abdomen remains swollen for several days and during this time, when I eat breakfast (no matter what it is), I have gas pains in lower abdomen. I am trying to understand why my stomach remains so swollen and if there is anything I can do to help return to normal. Thanks in advance for your help!