Rare bowel movements

I am 42 and have never ever had normal bowel movements.  I take them infrequently, maybe once every two weeks.  I have gone an entire month without passing a bowel.  I have a normal diet.  I have asked doctors about it and they are not very concerned.  I had a colonoscopy and they found no polyps or whatever it is that they look for.  The tell me to drink milk of magnesia every day.  I never have pain so I forget to do so.  With this much buildup in my system my whole life, am I more likely to develop cancer?  

[Caryopteris]

I don't understand why it doesn't feel like you have a bowling ball in your pelvis.  

It does not seem good.  You could speed things up with Miralax instead of milk of magnesia.  

You could get tested for Celiac disease.