I think I can relate to your situation as I too felt the same way when I was your age. It seems that you are wondering what is your purpose here, why were you, or anyone else is born? The answer to this question can be very depressing to some but at the same time it can be very liberating as well. The thing is some things are born with a purpose, for example the mobile phone I am using was born or made with a fixed purpose, a water pot is made with a purpose but we, human beings, are not. We have no purpose, we were just thrown in existence. But does that mean that we are worthless, that we have no use, that we should not live? No, it doesn't. It means that we are free to choose, or rather make our own purpose. We are, in a way, master of our own destiny. Whatever you do, or whatever I do writes the purpose of humanity on earth. So my friend, my advise to you is that try not to find your purpose here, you won't find it, make your own purpose.
Now coming to more immediate problems that you are facing, you say that you are not doing well in academics but this might be because you are not in the right stream, as it happened with me. I thought that I was a bad student but when I changed my course stream in graduation I found myself to be a good student, so you too can change your stream to your own liking in graduation, I think that you are someone with a bright mind. About books, you can buy am Amazon Kindle, on Kindle you can read books without giving any strain on your eyes, as it has a paper like display and it doesn't work like phone displays. I own a Kindle and I can read on it for hours without getting a headache, you can try it.
Just know that you are better than this, and keep on going soon you will realise you are better than you thought.