Have you tried Betaine Hydrochloride? I used to have terrible chronic constipation to the point that I would have to use enemas every few days because so little was coming out. I noticed large undigested bits of tomato, corn, mushrooms, and other foods were constantly present in my stools until one day my doctor told me to start taking betain HCL as well as digestive enzymes with each meal. Following the doctors advice I started having full formed bowel movements with much fewer undigested bits within a week of beginning. At first the stools came infrequently but as months went by my bowels started to function better and better until half a year later I concluded that I was cured.
I was brimming with energy and my bowels were functioning perfectly but I took it for granted that I was Permanently cured. I took too many courses in college, started running half an hour each day instead of walking that same amount of time, pulled allnighters which really hurt me bad, and also drank too much alcohol which was much less than you would think; my health crashed because of all the bad decisions and my bowels took three months to start functioning with regularity again. It took four months from the point where my bowels came online for me to feel as though I were cured again. I thoughtlessly started work around that time, I didn't exercise too much or stay up all night for work but I did drink and end up in over my head with the number of shifts I had to take. Four months into the job I started feeling the fatigue and brain fog dragging me back down but I managed to keep going another eight months until eventually I had to quit, again my bowels went from producing one to two large movements per day to a dysfunctional state where I had to fight to keep up. Right now I'm six months into staying home all the time and my health and bowel function are just getting back towards normal levels of functionality.
It's the damnedest thing though that each time my health plummeted it happened over the course of a few days, there was the warning of fatigue and brainfog seeping into my consciousness for months but my bowels would function fine through all that time, then, all to quickly, my health would just crash, my bowels would give up, and my fatigue would become unbearable all at once. I should have quit college/work the day that fatigue came back instead of toughing it out and ultimately crashing.
I have been taking the betain HCL and enzymes with almost every meal since I started two years ago and haven't found any other remedy of significance since then except maybe probiotics which I haven't adequately tested to truly advise their use and niacin which I used to take 1-3 grams of on an empty stomach before going on a walks or otherwise lightly exercising. Note that niacin causes flushing but somehow that flushing ended up with me feeling better; haven't taken niacin lately because I have been trying to test out treatments one at a time to get a better idea of which ones work.
If you do start taking betain HCL make sure to research it online, they say to start with a low dose and, over time, increase the amount taken until a warm feeling/stomach discomfort is felt then maintain a dose just below the dose that caused that. Do look up instructions though cause there may be more to it than that. I'm just starting to experiment with taking more than one tablet per meal recently, note that I have only ever taken Betaine HCL in tablet form and always right with the very first bites of each meal so I don't know if the capsule form should be taken at the start of the meal or somewhere beforehand to give the capsule time to break down. Note also that the form of Betaine HCL I take contains papain and bromelain which are enzymes that have never come within my digestive enzyme supplement mix so it could well be one or both of those that is causing my health to rise or it could be the digestive enzyme supplement but I kinda doubt it