I'm so sorry you are going through this horrible suffering. I wish I could give you some advice that would help but you have me stumped. I will bring up some points, though.
Have you ever had an upper GI done? I remember reading that it felt like fire burning down your intestines. You could have an ulcer. Those are very painful.
My neice had severe pain and D. She had a colonoscopy, they found she had some kind of infection and put her on antibiotics and that took care of it. But, you have had a colonoscopy and nothing showed up. (she also took Vicodin and was constipated from it)
Make sure nothing you are eating or vitamins or gum or mints, etc. has sorbitol. That's a big IBS trigger.
Have you considered changing doctors or do you think your's is doing a good job?
Sorry, but this is all I can come up with but I do think this site will help you work through this and you will get better.
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Re: Help. Me. Please. Now.
you are going through this horrible suffering.
I will bring up some points, though. 
