Long term side effects of Colace (stool softener) on the lower bowel

I am presently using Colace for cronic constipation. I take two in the AM and Two in the PM. It does not seem to be working anymore. STOOLS ARE SMALL AND HARD AND DRY. Yes I drink as much water as I can (the water goes right through me)...yes ihave seen my doctor. Is ther any evidence that long term use of colace effects the bowel in negative ways that would increase the problem of hard stools? I am a 54 year old male with hemmroids.