maybe you need to remind yourself WHY you workout in the first place.
if you wanna get in shape for the summer, remind yourself that its' only a few months away, or if you wanna get stronger, start using a journal and keep records of your progress, go for personal records once in a while, or if you been working out for a long time, take a few photos and compare to your old photos and see the difference etc etc
or, you might need a break maybe you been doing it for too long, or you might wanna mix things up, new routine, new exercises, maybe a training partner or whatever...
there's many things