You are not squinting for your values, or shadow patterns. Your shadows are too light and there is not enough contrast between light and shadow. Look the attached shot. Use rapid eye movement back and forth between your painting and the photo. Look at each part individually to check. Look at the nose in your painting then quickly look at the nose in the photo. back and forth. compare. train yourself to see where you are off and then fix it. Squint when you do this too.