Have you ever done a FULL and thorough bowel cleanse?
Simply taking a "gentle" fiber product like Flax, will indeed help things move along...but it won't do the deep cleaning of the lining of the colon that is necessary for strong bowel health.
So ultimately the 'gentle' fiber products usually cease to work because the root of the problem has never been addressed and/or healed.
I highly recommend Dr. Schulze s Intestinal Formulas #1 & #2 for deep thorough cleansing, but there are several products on the market to choose from. Let me know if I can offer anything further.