What should i do after a change in bowel habits (constipation), discomfort and a feeling of fullness or incomplete bowel elimination?

Doctors can examine: An older adult with constipation needs to be sure there is no other disease causing it. If constipation is just due to slow movement of food and poop through the gut, then the things to try are vegetables, water, fiber with water, prune juice, prunes, polyethylene glycol, Senokot or other senna, milk of magnesia, other laxatives... A doctor can evaluate to check for anything serious like cancer.