I started having digestive problems after steroids which gave me ulcers and kicked off NSAID gastropathy so I had to (permanently!) stop taking the meds for my back pain. I also discovered I was lactose intolerant at the same time; no idea if it is related or not though. The gastroenterologist prescribed omeprazole to sort the ulcers out. It might have got rid of the ulcers, but I was still having painful spasms and nausea. He then prescribed spasmonal forte for what was assumed to be nerve damage from the ulcers. He thought 4 weeks worth would be enough to allow repairs. It helped massively, but as soon as I stopped it, the problem came back. Happened to see my neuro that week. He told me that although most people think of the digestive system as a standalone system, the central nervous system has an input (the vagus nerve) and that problems with it mean that many people with MS end up with IBS diagnoses because the gastros can’t explain their symptoms. He also told me that if the spasmonal forte worked, to just keep taking it. So I do!
Next thing was chronic diarrheoa. I went to see the gastro again, was dx’d with IBS(!) and prescribed loperamide (which is the active ingredient in Imodium). I now take one every evening and it does the trick to slow everything down (and has the extra benefit of allowing me to eat some milk products again :-)). Of course, having one extreme is easier to deal with than swinging between both, but perhaps loperamide might help you when you need it?
If your gastro/neuro/GP is OK with it, I’d have a go at spasmonal forte if I were you - it’s like baclofen but for involuntary muscles (i.e. muscles that you can’t control) and it’s been great for reducing my stomach spasms.
BTW, given that you’ve got terrible fatigue too - it might be a relapse?