Hey Tuna, I like the stylized way that you drew the face, it's very interesting. I think though your problem with realistic lighting has to do with your drawing. You must create solid 3 dimensional forms in your drawing so that the lighting will make them feel more realistic. Once you have solid forms with side, top or bottom planes, you can light them in a more convincing way. I did a quick sketch of you painting to show you what I mean, I hope it helps :)