Slight on and off pain on top of belly button or in middle of stomach no other symptoms what can this be. Hope its not appendicitis?

Doubtful. If the pain has been there for more than a few days, its unlikely to be appendicitis. It could be a hernia at the belly button, or just above. This is especially true of there is an associated lump that can be pushed in to the abdomen. Best to see your primary care provider for a more complete evaluation. Timing depends on duration and severity - longer and milder, less urgent. Hope this helps!