Yesterday, I noticed a slight lump/bulge on my upper left abdomen below my rib cage after dinner. It is not painful. Is this anything to worry about?

Not yet. I wouldn't worry too much just yet. It could be a harmless cyst or deposit of fat called a lipoma. It's something your doc should check out - not urgently, though. If it's not painful and you have no other symptoms, it could be done within 1-2 weeks.