Hi there,
From what I see I strongly suggest dropping the drawings from imagination and thoroughly copying reference for a while. Not only the linework. The complete set, values and all. Working in greyscale is a good idea and as you can handle Photoshop it might be good to focus on digital for a while. Open your source photo side by side with the canvas and start to draw what you see!
Which is why this book might be very helpful as it focuses on making you draw what you see as opposed to drawing what you think you see.
For the portraits: Try to find reference which has other views, too. Not only the frontal view. A nice 3/4 view offers nice opportunities for shading and showing the character.
I like the b/w digital eyes, btw!


































