ok - to try and avoid this happening again, always trade directly from your party rather than from a box. you have to bear in mind that people have put a lot of care and attention into breeding these eggs for the swap and switching them out for one of your own is not a good thing or something to be done lightly. if you ever get you egg back (the text will read 'welcome back egg!'), then i suggest you switch it out for the one you originally got. does that make sense?