Lipstick and Knickers by Rosen Trevithick

The morning after being out partying with friends Ross wakes up hung over and with little memory of the end of the night before.  As he gets up and heads to the bathroom he finds a pair of ladies knickers on his bedroom floor.  In the bathroom he finds a lipstick on the sink.  Ross is in love with, and hoping to marry, Lizzy.  The knickers are not the type that Lizzy wears.  

Ross is in a panic about what has happened and sets out to find out who he spent the night with.  One by one he meets and eliminates women he remembers from the party.  

This was a free kindle download.  It is a short story.