I've done nearly 300. I still can't crack Google or Facebook etc and I'm still extremely depressed that I"m just inherently unable to because my CS education wasn't good enough (because I wasn't good enough to get a better SAT score etc etc). I work at Amazon, so I know what the "elites" think of people like me.
I've gone and reread Skiena, etc but the end result ends up just my eyes glazing over proof notation and crying.
Sounds to me like you're focusing on the wrong things or don't have the right resources for the task at hand. (that is, I don't think I've ever had to brush up on a proof for any algorithm or data structure when prepping for interviews)
Take it from someone who also had a shit background/education in math/CS and had to teach myself a lot of these things from scratch - it's doable, you just need time, and I guess the mindset that you can learn these things. See my comment history for some book recommendations. If you really feel like you need to learn things from scratch to give yourself the confidence of having a solid foundation, look at some of the intro computer science courses on Coursera. When I realized most of my uni's cs courses were... not great, I just ended up going through courses like Stanford's Introduction to Algorithms on Coursera and teaching myself.
I can also tell you as someone who was in Seattle for a while and had a bunch of friends at Amazon, I don't think anyone is going to think less of you, if anything, being able to survive at a place like Amazon seemed to be recognized as its own accomplishment...
edit: I'll also add (from personal experience), if it still feels like these things are difficult even once you feel like you have all the right resources, look into seeing medical professionals to make sure you're not being held back by anything, like sleep apnea, any cognitive disability (not sure if that's the right term...) etc
I've gone and reread Skiena, etc but the end result ends up just my eyes glazing over proof notation and crying.