Hi,
 *  Pain in left side of abdomen along with 
constipation indicates -
     - diminished intestinal movements due to advanced age.. the stools being held in intestines for along time.. the water within gets absorbed & cause dry /hard stools , difficult to pass ,stagnant / hard stools collected in 
rectum... causing plenty of gasses/ bloating/ pain. 
    - Infection of bowels ( amoebic/ worms may cause constipation.
    - strain to abdominal muscles while strain for motion. Over straing causes hemorrhoids.
  * you can try to attain natural evacuation of bowels by-
       - Specific  Treatment of bowel infection after investigations / doctor's advise.
      - Having high fiber diet ( vegetables, salads, fruits, avoiding refined grains/ pulses)along with lot of water through out the day. & avoiding fast foods having refined flour.
      - Drinking 2 glasses of warm water first thing after getting up in morning.
       - Routine walking & abdominal 
muscle exercises,
     Thanks.
      - Forming a regular defication habit.