IBS can certainly be considered. You can also consider pancreatitis as well as inflammation of the upper digestive tract or an ulcer.
In addition to the tests you have already had, I would consider an upper GI series or upper endoscopy to evaluate for these other causes.
Another consideration would be untreated GERD. A 24-hr pH study can evaluate for this possibility.
If negative, then IBS can be optimally treated. You mentioned that Zelnorm and antispasmodics have been used. You can also try tricyclic antidepressants which may have some success (seen in small trials).
These options can be discussed with your personal physician.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Kevin, M.D.
http://www.straightfromthedoc.com
I had a lower examination (I forget the word) colonoscopy and also endoscopy and it did reassure me that my insides were ok. I am willing to say it is hormones and diet. The biggest advice I can give, which won't hurt, is to eat bland, regular meals, eat enough, exercise to feel good, and above all, try to avoid stress which will make your female hormones go haywire and might aggravate symptoms.