IBS sucks, IBS can be diagnosed succesfully based on the symptoms, minus red flags. Even with no diagnotic marker.
While some symptoms of addison's disease as well as quite a few others may mimick some IBS symptoms, there are still ways to seperate the two.
You certainly can ask your doctor.
I woud also read this page carefully.http://www.aboutibs.org/site/about-ibs/symptoms/
Part of the problem also here is there is evidence for a problem with the HPA axis in IBS as well.