Your drawings have such a sense of realism! Your way of drawing hair look so natural. But you feel you are failing a lot. I don't know if this is a good idea, and maybe some of the more experienced artist should agree or disagree with me before you do this, but: Try different styles, maybe something a bit more sketchy, something more artsy, something fun so you can draw from imagination. You won't achieve photorealism at once without refs, so it tends to look too stiff and boring maybe. That hover cycle pic you posted from imagination was stiff and a bit boring. Try to have more fun with the imagination instead of being stressed about your performance!