Have you tried lots of vitamin C? It works great as long as you use non buffered type. I use 1000 mg vitamin C with hydroquercetin from Life Extension Foundation. I do 4 grams a day, spread throughout the day.

Of course vitamin C (and quercetin) are very powerful antioxidants so they are good for much more than constipation.

Drink lots of water too, but I bet you knew that.

Also if you're concerned about smooth muscle movement take some L-arginine. I do some of that too.