other artists already offered great tips on dealing with loss of motivation but I feel it's mostly for short-term or just a quick loss of motivation for about 5 minutes.
If it's long-term (like say around 3 months and this keeps happening again and again), then it's best to not do art at all and just go and explore around place you found inspiration at. Sometime, we have to go back to what got us into art in the first place.
For example, I do cartoon cars but I sometime forgot why i like doing cars in the first time. it wasn't till I saw a random car show when I saw some exotic cars which made me remember why i drew cars in the first place. And bam, there goes my motivation to draw cars again!
There are many other ways of combatting your lost feeling/motivation but the key things like others has said is to find out why you like drawing in the first place.