Hi there, u r problem has more to do wid concentration then wid memory ....sometimes when we r doing a task which requires attention but our mind is attending a totally different thought ...then we tend to not register the task or command told at dat time...
later when we try to recall the same ..its quite obvious dat u won't find it becos u never registered it....so ur problem is related with being preoccupied wid thoughts of a different context ....this may be due to stress - physical or psychological.
Going through a detailed discussion regarding the same can help u focus back on life . Feel free to consult on a convenient occasion wid a psychiatrist of ur faith and approachability.
Hope dis helps u but feel free to raise any further queries...thank u.