I gave blood today.  For the first time!  I beat my dad as well.  Started after him and finished before him.  That made my day


Random riddle now.

There is a word that's singular.
Add an 's' and it becomes plual.
Add another 's' and it becomes singular again.
Add 'es' and its plural again.

What is the word? 
(yes they all have to go on the end)