The strict definition of IBS is outlined in the ROME III criteria and includes only this:
IBS is a functional bowel disorder in which abdominal pain or discomfort is associated with defecation or a change in bowel habit, and with features of disordered defecation.
Clinically it is described this way:
Diagnostic Criteria* for Irritable Bowel Syndrome
Recurrent abdominal pain or discomfort** at least 3 days per month in the last 3 months associated with 2 or more of the following:
1. Improvement with defecation
2. Onset associated with a change in frequency of stool
3. Onset associated with a change in form (appearance) of stool
*Criteria fulfilled for the last 3 months with symptom onset at least 6 months prior to diagnosis.
**Discomfort means an uncomfortable sensation not described as pain. In pathophysiology research and clinical trials, a pain/discomfort frequency of at least 2 days a week during screening evaluation for subject
But all this is basically only useful to tell you that you have IBS, which circularly means you have these symptoms. Not at all helpful. If you have IBS symptoms and nausea, you can probably find out what is causing your problems and treat it. But you will need to work with a doctor who pays attention to the research and actually does the (unfortunately rare) testing for all the known causes of IBS symptoms, nausea, GERD, etc. I always recommend the IBS Treatment Center in Seattle (IBSTreatmentCenter.com) because they helped my wife and a number of my friends. It is the nation's leading center for the treatment (not just diagnosis) of IBS.
Um, I live in Seattle and I've never heard of this place. Where is it?