I put my guitar away for 20 years and just picked it back up 8 months ago. So I know the feeling of losing interest. Now when I have a few days I'm just not in the mood to play I take my electric unplugged in front of the TV and just run scales and next thing you know I'm trying to put together a new riff idea. Next thing you know I'm plugged in and trying to expand on the riff. Try it next time you feel like quiting or lack the drive to play.