The practice of mindful living should be joyful and pleasant. If you breathe in and out and feel joy and peace, that is Right Diligence. If you suppress yourself, if you suffer during your practice, it probably is not Right Diligence. Examine your practice. See what brings you joy and happiness of a sustained kind.
Oh, but nothing gives me sustained joy and happiness. How can joy and happiness guide me when I don't experience them?!?