I'm trying so hard to study for the SAT tests so I can get into college next fall, but I am struggling with retaining knowledge.

It's hard enough to get myself motivated to study and I even have to go to the library just to get anything done so I don't get frustrated and default back to playing video games, watching anime, or hanging out on PC.

What's making things even harder for me is that I simply can't retain complex information no matter how hard I try. I get easily distracted and daydream when I get bored and when I am finally able to sit down and read a chapter or two in a text book or watch a few videos on Khan Academy, I have trouble remembering everything that I read or watched.

I know a big reason why I'm like this is because I am so behind on a lot of my general education, particularly math, and as such, catching up feels like doing an entire 4 years of math coursework just to be on an equal footing with everybody else which is making it difficult for me to even care.

Still though, I was wondering if I can get over some of my memory retention issues off changing my diet. I can't afford to eat whole servings of fruits and veggies every day so I rely on supplements to fill that void at least somewhat. I also eat a lot of tuna and I buy those dollar pasta sides bags and mix tuna with it to make tuna alfredo which I eat every day as a primary meal and I consume protein shakes for breakfast made from this soy protein shake mix that I buy at Walmart because it's only $10 for 15 servings. Other than that, I fill my diet with soups and sometimes frozen burritos when I'm feeling starved after donating plasma which isn't healthy but my options are limited due to financial restrictions.

Most days I struggle to reach 1200 calories and on average, I consume maybe 700-800 at most.

Could this be the source of my memory retention issues and possibly my moodiness and lack of motivation? If so, is there any cheap ways for my to solve this problem? If I do make such a change to my diet, would it improve my ability to study and retain information? If so, would it be a significant difference?

Sorry if I'm rambling at this point it's just frustrating dealing with all of this when I have a hard enough time as it is just getting through the day.

Thanks.