This is a bit of a long shot but its worth mentioning.
3-4 times...normally the day after I have done a liver flush, I have passed objects that are almond shaped and size, but yellowish in colour. these are very hard on the outside but when dissected seem to have white chalky stuff in the inside. I reckon mine are some form of compacted calcium that comes out as part of the liver flush. a Liver stone I suppose....but calcium rather than cholesterol!
As I said.....its a long shot. other than that undigested food......its really too big to be an egg as you have said.