Does protatitis cause bowel movement problems like constipation or diarrhea?

Prostatitis treatment can. If the prostate is enlarged it can affect bowel movements. I have seen problems with the bowel affect the prostate.

There are other factor far more likely to explain constipation than an enlarged prostate. You may take a fiber laxative like Metamucil and drink enough water daily so that your urine is colorless. For the long term you may try to increase your intake of fiber foods. http://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/high-fiber-foods/art-20050948