Tiggeroo,
I'm glad you are getting the colonoscopy exam. As you probably know, IBS is a diagnosis of exclusion. Meaning, when they can't find ANYTHING else wrong with you and you have symptoms, you will finally get the IBS diagnosis. I really, really hate it when I doctor slaps this label on a patient but does not do a full workup. I had unremitting diarrhea for 2.5 months and two doctors told me "You have IBS." I finally went to a gastro doctor and he told me, within 5 minutes, "no, you have a parasite" and my diarrhea was cured in a week. This was after a 25 lb weight loss and 2 months out of work. I was pissed at my other doctors.
Anyway, if your colon is spasming hard enough, you can get back pain. I posted a site earlier on IBS. I think you should visit it and post some of what you are feeling. I think, there, you will probably find someone who suffers the same problems. If you don't want to post, just read. It is very informative.