What Causes Intermittent Abdominal Pain And Bowel Irregularity?

I recently experienced about a m6 weeks of intermittent abdominal pain and bowel irregularity (days of constipation, followed by a day of diarrhea). I had a colonoscopy, and everything is normal except for an unusually twisted ( tortuous ) colon. My doctor advised taking Purelax (or equivalent) every day, indefinitely, to prevent constipation. I am worried about becoming dependent on it, or having other ill effects. I already eat a very high-fiber diet, plus I drink lots of fluids. I am a 60-year-old female in great overall health. What is your opinion? Thanks.