How did it end up like this?

First day of semester tests was today. I got a high enough grade to get an A in precalc which made me really happy! :D English was a breeze of coarse. And then there was chemistry...

I got a D on the test giving me a C in the class overall. I've never gotten a C before. When did I get so stupid? It kills me.

I'm finding more and more reasons to hate myself.