Yesterday I just did my third colonic/infrared sauna in a series of 12 that happen weekly.
I had the opposite problem as you. While I didn't have diarrhea, I was going three times a day for the past year and it was really loose.
Now I go 2-3 times a day, it's solid and the stools are rather large. I can imagine if you are constipated, colonics
could only help you.
I'm starting to notice a little difference now after having three... feeling better... though I'm positive that it also has something to do with the mostly organic food I'm now eating.
I'm not a doctor or a healthcare professional, but I would suggest looking into colonics. In my unprofessional opinion, they can only help you, especially in your situation.