Well your pixel art there doesn't look that bad. I mean there's a bit of issues with proportion and such, but you clearly know SOMETHING about anatomy, and the 3d aspect works for me with it.
I think your to hard on yourself. I've been there a million times. I'm 21, I've been drawing since I was 10, and I STILL can't draw the way I thought I would by now (Professionally.) People say "practice, practice, practice!" Well I always said "but I DO practice! I DO!" But if I were really being honest, I wasn't practicing as much as I should. I wasn't doing the recommended 5 studies from life a day. I wasn't going to any life drawing sessions, and I wasn't really pushing myself the way I should have. So today I'm 21, and my potential hasn't decreased. The answer is still the same, if I want to draw like a pro, I have to practice like a pro.
So here's what I recommend -
Draw nudes, a lot of nudes, all the time, draw nudes! NUDES NUDES NUDES!
Draw them from books, draw them from your comp, draw them live from classes and studios.
Draw them every day, draw them every way, draw them in your house, draw them with a mouse!
Also check out burn hogarts book on perspective, it's amazing and will push you over the edge.
Another book I recommend is - Atlus of human anatomy by stephen rogers peck. It's thorough, and if you read it, you will have a thorough understanding. Don't just draw a few bones, MEMORIZE them! Bones are more important than knowing muscle. Learn the muscle next, and memorize that.
So when I sit down and practice drawing, this is what I do-
3 30 second gestural drawings (gestural drawings are done to capture motion and what not, and are done fast.)
I do a few 5 minute nudes.
I do a 30 minute nude.
If I'm having trouble with anatomy in an area, or I want to learn how to draw better noses, I additionally study anatomy for that area of the body, and I draw a thousand noses from references that day.
If you do this every day, 7 days a week, you will be a pro. If you want to be a pro, you have to practice like a pro.
Good luck!