Careful not to outline. This is the main culprit that robs depth. You can do some but vary the thickness of that line depending on where you see shadow. Draw line through the body as if following the surface. Practice those 3D shape line drawings. I can see an interest in shading. Stick with that but try to do some drawing without line as well. See if you can get to the same point without it. Also practice gesture. Look at some of my figure drawing and try to loosen up a bit. It will look weird at first. After a while it will add a lot of life and dynamism to these. Last one is my favorite. You're getting the weight. Keep drawing heavy forms. There is natural talent there. I can give you some pointers on face shorthand if you would like. Email me. Keep drawing!