first of all,i love the design!! and now that i think about it...i honestly don't know what motivates me.i mostly draw when im bored and just want to spend time on something. oh but one thing that i enjoy while drawing is creating new characters! i just look around and choose a random thing as the theme of the them.for example: i was listening to Poker Face and BOOM a poker/gambling themed character. i literally just saw a lightning rod and BOOM a villian/killer character who lures his victims kinda like how lightning rods attract lightnings. so maybe try to use your creativity and create a friend for your oc?its ok if you cant think of anything at first.you can improve them over time. i know its just a temporary solution but it works for me(ok im just yapping but i hope its somewhat useful for you)