What Causes Chronic Constipation Without Laxatives Despite A High-fiber Diet?

I am a 59 year old woman been on antidepressants half of my life and going through menopause for the last five years I have taken all types of laxatives to promote a bowel movement if I don't take the laxative I have no urge nor sensation to have a bowel movement I recently had a colonoscopy the diagnosis internal hemorrhoids on a high fiber diet fruit grains and nuts vegetables and six to eight glasses of water per day the . results manage to lose weight and stay gassy and bloated. .