If your serious about art get used to that feeling. I worked so hard to draw like I do and I still see some art that just blows mine right out of the water damn, but your best lesson would be persistence, and the opposite knowing when to stop. ALWAYS put a piece down when frustrated with it and never let art feel like a chore. Also if your serious the best way to get good at something is to do it everyday. It's really all about finding a balance. I'm not a pro but this is really general advice. Not that you need it or anything. I'm just reading your comment.
How long is a long time? Do you draw without references? That's normal people think it's their hand they are training to draw and part of it is that, but mostly it's your eye. Your attention to detail and being able to see mistakes accurately and knowing how to fix them. I'm not really the best person to get advice from but trust me keep at it. Always study your subject look at how one line or feature connects into another, and always use references. Some people don't need them but it takes a while before they can draw without them. I notice my best art is always dome with references. Don't underestimate guide lines and those circles you draw in the beginning they are important and do help. Most importantly keep at it.