Have you thought about getting your thyroid checked? Or making sure you are getting enough magnesium?
Not having a bowel movement is a common problem with hypothyroidism as is low magnesium levels (which by the way hypothryoidism brings on).
I had that problem years ago and I ate all sorts of fiber and water. Turns out I had hypothyroidism. When I got on meds and was also able to get my magnesium levels up, the problem went away.
Calcium/magnesium help with peristalic action - calcium causes the muscles to contract while magnesium causes them to relax. If either are too low, you'll have problems.
Not sure if this is your issue but it's definitely worth reseaching, just in case.