Being exhausted from drawing?

I know, people say you have to draw more then 6 hours every day to become an professional artist. What I am doing is basically exactly that. As soon as I'm coming home from school, I eat something and learn what's needed, maybe skip something as well. I turn on my pc and I begin to draw. I make breaks every 30-40 minutes for 15 minutes or so and keep going. That's what I do for almost 2 months now, but I somehow feel bored and exhausted when drawing. I think at every pencil stroke how can I make it better, is that line right, maybe change some colour etc.. When I am not drawing I think about drawing and how I can get the most out of my time. But really, is that the way to go? Sometimes I want to play some Overwatch but I just dont want to end up playing 2 hours straight. How much drawing is needed and how much is not enough? Everytime I finish for example the pants or a weapon of a character I have to make a break because it takes so much power...