After gaining some weight a lump bigger than a golfball is always protruding from the navel. could it be anything other than a hernia ok to ignore?

Rare, but yes...: It could be something else. Your description fits a fair number of differential diagnoses (possible medical conditions). The information needed to confirm or rule out each possibility include: symptoms, changes in function of different organ systems, physical examination, labs and radiologic studies. Some of the possibilities are quite serious, so i think it is not ok to ignore. See your doc.

Probably a hernia: Hernias can get larger, cause pain, or become acutely incarcerated and strangulated (gangrene). See your doctor for an exam and advice for your specific circumstance.