I had a sudden swelling on the left side under waist and slightly forward, size of baseball. Some discomfort and pain. Thought

My bowels remain perfectly regular, no blood in stools, no severe pain, no fever, no symptom other than localized swelling.  Three doctors diagnosed hernia needing surgery.  CT scan ruled out hernia and cancerous tumor, leaving diverticulous.  I'm puzzled since I can't find any reference to similar swelling.  If it is diverticulitis, does it indicate any perferation or need for surgery?