Hi, I have had the same exact problem for many years. The past 17 being the worst. I am a Nutritionist,47 years old. First of all, make sure you are not eating ANY dairy products of any kind and that you are eating lots of raw fruit, vegetables, and whole grains like oatmeal, brown rice, whole wheat bread and whole wheat pasta. NO refined grains like white bread, white rice or white pasta either. Try using Ducolax brand rectal suppositories. Not regular rectal suppositories. The Ducolax laxatives are the only ones that work for me also (I'm talking about the oral ones now). Ask your Gastroenterologist to give you a "colonic transit test" if you haven't had one already. If this test shows that you do indeed have colonic inertia, you will next need to have a test called a 'defocating proctogram." This will tell if your rectum is working. If it is, your lucky because that would mean that even though your colon is dead, your rectum is not. That means that you could have your colon removed and they could hook your small intestine up with your rectum. You would be able to go to the bathroom normally. You would not have to wear a bag. If you wait, and you keep dealing with this problem for years on end like I did, your rectum will weaken and it too will have to be removed. Your pelvic floor will also become very weak. This is where I'm at. I waited too long. Now my colon and my rectum have to be removed so they must make a fake rectum called a J pouch. These work well for most people but not for people getting them due to constipation problems because our pelvic floors are too weak for them to work well. So, I will most likely end up having to wear a bag. So please, don't be like me. Get the Defocating Proctogram test and if it is normal, consider getting the surgery NOW. Also, have you tried bio-feedback with a Physical Therapist who specializes in pevic floor and bowel dysfunction? They have them at U of M hospital in Ann Arbor Michigan where I live. Try to find one at a hospital near you. Make sure they specialize in BOTH pelvic floor dysfunction AND bowel dysfunction. Do this before trying surgery. But get the 'defacating proctogram" test regardless. Good luck and I hope this helps.
Have you tried taking probiotics? Along with the high fiber, dairy-free diet, you should be taking probiotics. Primal Defense by Garden of Life is the best brand (trust me on this). Some times, just the diet and the probiotics will relieve the constipation. And they always help, even if it's just a little.