Hi @nickhoo what you are feeling is actually a common thing so don't stress. The feeling of not getting better is tied to the fact that your eyes (art knowledge , being able to pick up on mistakes ect) and hands (mechanical skills and techniques,) mature at different rates. A time feeling like your work is just getting worse is your eyes and knowledge progressing faster than your technique which will eventually catch up as time goes on. Sorry for the wall of text but it's a common issue that you will face your entire life as an artist and it's handy to know about it sooner rather than later.
Now onto crit for the piece. The anatomy of the neck down seems pretty solid with proportions and the pose overall. Your head anatomy however needs works. The hair line is half way down the forehead, the ears are to high they should align with the top of the eyes and bottom of the nose as a general rule. The hair could also do with loose strands and details that don't make it so uniform.
I would suggest looking up the Proko series and vid on how to draw heads from all angles and to get a better grasp on the form. I think Cubebrush might also have a vid on this subject.
Great work overall and a desire to improve and look for crit is amazing and will help you rapidly improve.
