It sounds to me like you're not drinking enough water/getting enough fiber. Irregular bowel movements can be pre-cursor symptoms to severe gallbladder problems, Pancreatic problems, Intestinal problems, etc. If you are getting enough fiber, and getting enough water (~ 1/2 a galon at least a day ), You should get yourself checked out. $40 at the docs could save a few grand on a surgery in the future.
A BM every 3 days is not healthy. 1-2 days tops is what it should be.