You're doing well! I agree with the others and recommend starting with more structure, such as the Loomis head and guiding lines. Get those height to width measurements/relationships down (and make sure to continuously check them because things can "drift") and then keep building the rest of the portrait from there. To help with shading, Block in the shadow pattern first so you have a clear two value read of what is light, and what is dark. Then from there you can add more values. When using charcoal or pencil, it'll take a couple passes of layering the tone to build up to those darker values. Looking at your drawing, you've done a nice job keeping the tone application even and smooth! I included a quick drawing of your reference, to show some of the early structural guides and shadow mapping I do when I'm drawing.

From my experience, it has helped me to research how George Bridgman and Andrew Loomis did the head structure, in order to get a better likeness. Also, the more you fail, the more you improve, as painful it can be sometimes, just keep on practicing portraits.

I find it really helpful to draw some guiding lines and really prep to get the proportions right. No harm in measuring a bit. The more work you do in the beginning making things go where they should on the face, the less you will have to erase and adapt later on. It took me a while to see the face as a whole, rather then individual parts, but since I have realized that portraits have become easier. Really, practice makes progress tho!