Dude! This is something that I struggled with when I first started studying. It was so overwhelming at first. What helped me the most was going to a specific location to study (library, for example) rather than staying at home. I also was careful with what I was eating to make sure that wasn't affecting my tiredness. I also packed some sweets along to eat and "feel better" and continue studying. I first started off by studying for 3 hours cause that's the most I could do and then as I kept doing the same routine, the hours that I could study increased ALOT! I think that I was just so used to my routine that I conditioned my brain to think "now is work time." When I started doing the practice material and actually learning from my mistakes, I found my studying much more interesting! The more you get into the studies, the more fun it will be. I went from being scared of the MCAT to actually enjoying studying for it! And this actually increased my focus time. The more time you spend on it, the more you get used to it and the more you get into it. I definitely took some days off when I needed to just to get myself together lol. This is just something that worked for me!