Welcome to HealingWell!
What you're describing doesn't necessarily fit the IBS criteria. Your case seems extreme. Have your docs had you swallow the camera pill so they can track your entire digestive system (all 30ft of it)? It's quite possible for you to have Crohn's and they haven't been able to find the inflammation site.
You should be working with a nutritionist to help you better figure out what you can eat and how to get your nutrients.
Do you take any probiotics or digestive enzymes?