Who laid the Egg?

Went to chicken coop this morning and found a little egg the size of a buck eye, no shell, and was wondering if one of the pullets could have laid it.  They are about 22 wks, or if the hen who hatched them out could have started laying again.  So I was wondering, who might have laid the egg?  When the mommy hen does start to lay again will her egg just be the regular size or will it be small?  I wasn't sure that's why I kinda figured it was a pullet.  Well, lot's to learn about.  Don't ya love Newbies?

Monty-- What would the "Chicks" do without ya? Thanks for the info!