Do you keep rehearsing your piece once you get it down? Even one day without practicing certain pieces will wreak havoc on my abilities.
Specify which pieces you are working on, maybe you are approaching them wrong.
Have a look here:https://www.pianostreet.com/smf/index.php/topic,7603.msg76044/topicseen.html#msg76044(a huge collection of links related to practising-kindly provided by Bernhard )