I just wanted to give some friendly advice,
If you want to really learn to shade well, I would invest in a set of different hardnesses of pencils to use for your drawings. This one looks like it was done using an ebony pencil right?
A good starter set of pencils would be a 6H, 4H, 2H, B, 2B, 4B, 6B
These go from a very light colored and hard lead (6H) to a soft and dark lead (6B)
This will make shading a lot easier.
I also had a hard time with my high school art teacher, she was a very different person from myself, and after a year of taking classes with her that I had NO interest in, I just asked her if I could do an independent study. This was probably where my passion for art REALLY took off. Now I'm about 1 year away from getting my masters, so keep at it, and remember that you sometimes need to be your own cheerleader.
Lastly, I would second the comment before on making sure you try to draw what you see not what you know. This is a hard thing for everyone to get past! Trust me!
Keep at it though! You look like you have a good foundation.