He's talking about insomnia. There isn't any specific reason given for it. However, the repeated line "on my own, here we go" gives me reason to think that maybe the insomnia is caused by being alone in the world for the first time and working just to make it to tomorrow, and putting your health on the backburner just to live.
its about meth... simple as that, talking about no sleep, being fucked up in his room, all alone, eyes gonna bleed cause he has been up for days he focuses on the no sleeping part of meth really.