Seeking Advice from Seasoned Players

I love this game. I have played 428 hours and don't plan on stopping. I have my early game down and can get to castle and boom in a very good time frame. I have memorized most hotkeys, understand the unit counters, and am very sound when it comes to game knowledge. However, despite all of my playing and comprehension of mechanics, I always run into a sort of wall when the late game comes around or if I am attacked in general. I become overwhelmed and feel powerless to act. I can hardly give my units orders, even when I know that I need to spam barracks and start massing halbs to stop the onslaught of Paladins I am facing. I get in this hesitant and useless state and all of my skill leaves me, which leads me to believe I may have none to begin with.

I am not really sure what kind of advice I am asking for here, but I was just hoping someone could tell me something, maybe a way they overcame this strange phenomenon when they were getting better themselves. My ELO is extremely low even though I can get to castle age and micro just as well as a 1700 player can. I always fall apart somewhere along the line...I need to break this habit somehow.