It's hard for anyone on here to offer much advice concerning the potentiality of you having a memory deficit. That requires psychological testing to verify. Some people just believe they are having recall problems. You being under stress from knowing you will be taking the the SAT soon may be a factor.

A suggestion for studying would be to invest in either books that are like a study guide for the SAT, or a service that would give you a crash course. Trying to do some random vids on khan academy is probably not going to get you anywhere.

What bothers me more is the fact you are putting your body into starvation mode. That has serious health risks if it goes to far. It can effect your heart (conduction system) and other vital organs. If you are a woman, the min you should be eating, unless a doctor tells you otherwise, is 1200 calories. A man should eat 1800. You need to see a physician and get some help with this before you go to far with it. You will have far worse than an SAT to deal with.