I've taken both Bentyl and hyoscyamine and both had side effects.
I could not stay on Bentyl as I felt STONED, and I stayed on the hyoscyamine for several months, but you may have to play with doses to regulate. I was experiencing blurred vision, cotton mouth and could hardly stay awake, to where driving was not safe. I ended up taking the meds at night, and broke the pills in half.
I am currently on Elavil, which is working well for me. I may be wrong, I think it is actually an antidepressant ( like the 2 others). It is very mild. Hope that helps