What Causes Vomiting, Severe Abdominal Pain And Fast Heart Rate?

Hi, my boyfriend has been experiencing severe abdominal pains that he describes as feeling like someone is stabbing him and he is vomiting acid, and he says he is also vomiting something that looks like yellow gumballs. His heart rate also increases rapidly when he feels shivers or when he is vomiting. He s had surgery before to take out his appendix because they thought that may have been the problem, but the problem is persisting, and he has been like this for the past year. The past few days he has been in and out of the emergency room. His doctors are saying that they don t know what the problem is, and with my mother being a doctor and me being in med school, neither of us know what is going on either. I ve spent the past few days researching for a diagnosis, but I m not exactly sure which one is fitting for him. If I could get a diagnosis from someone, I would be better equipped to help him and know where to take him. He is 22 years old...