Struggling with Pain: How to Keep Going?

How am I supposed to just keep pushing through the pain? It's excruciating, but I have to go to school. I would take a day off, but I'm going to be in pain for at least a week, and I can't take a week off, so I'm saving that day for when I really need it. How am I supposed to just push through? I'm here, but I can't even focus. I feel awful and it's so unfair. Nobody can see how hard I'm trying, they just see me "spaced out" (in so much pain I can't think straight). I'm trying not to think about how it's not fair I have to deal with this, accept that this is just what my life looks like, and keeping going, but it's so hard.