Do you know how much fiber you are getting in your diet daily? Also, what do you typically eat? The best things for constipation are fiber, more water, exercise if Doctor approved, and other nutrients. You should eat more leafy green veggies. Try eating a large raw salad a day. I use spinach as the lettuce in my salads.
You probably just have a *lazy bowel.* I have had this my whole life. I take stool softeners and eat yogurt and fiber. If the colonoscopy came out OK, I wouldn't worry. You can also try a fiber supplement like FiberCon or Benefiber and see if that works.