I feel pressure and occasional pain in the left lower abdomen and left side. Any ideas?

Diverticulitis. Get a cat scan to prove it. Colonic diverticulosis ( tiny balloons protruding out of the colonic wall ) are famous! in the sigmoid and left sided colon. Clear liquids for a day or two and a 10 day course of Levaquin (levofloxacin) will do the trick. If the ct scan is negative, have a colonoscopy.
Could be. Constipation or diverticular disease or colon growth, inflammation. Please see a gastroenterologist or colo rectal surgeon for a thorough evaluation.