I am so sorry you are miserable! I have the exact same issue and underwent a colonoscopy and other testing, nothing was found to be causing my severe *C*. The only thing that works for me is Milk of Magnesia, and I take it the night before. It works fairly well for the most part. My *C* started and then became progressively worse in a span of around six months I would say, and it just went from there. Pretty soon, I was unable to get by without laxatives. It is a vicious cycle! I hope you find out the cause of what is wrong!
I also get the horrid stomach rumbling/noises that goes along with it, but the only thing that quiets that is prednisone. Gas X does nothing!