Diverticulitis is a condition when small bulging pouches (diverticula), formed in the lining of the bowel, get infected or inflamed and cause discomfort. Diverticulitis can cause severe abdominal pain, tenderness around the left side of the lower abdomen, fever, nausea, vomiting and a marked change in your bowel habits. Mild diverticulitis can be treated with rest, changes in your diet and antibiotics. Severe or recurring diverticulitis may require surgery. Surgery for diverticulitis involves removing the diseased part of the bowel.