Why, on the second week of school, am I so discouraged?

It's the second week back to school, and I'm already worn out for the entire semester.  I feel so helpless and stupid at this point.  My depression/anxiety gets pretty bad during fall because of school, I usually am very happy in Autumn, my depression used to subside a lot during Fall, but now, my workload is so heavy, and I feel incapable of completing school.  I keep on pushing, but it will take me and hour to finish 15 math homework problems.  I feel so hopeless.  I feel useless.  I'm already modifying Math and Latin, because I'm behind. My mother, instead of privately going to my teacher, decided to literally yell across the room, in front of all my classmates, as we left orientation, that I was still in last year's math.  She decided to leave the fact why I was still behind out.  It takes me a half hour to understand a new concept.  I'm so slow and stupid.  All I can do is sit around and be useless because I don't understand.  I just sit around staring at the wall all the time, thinking myself to death.  I just sit and think, think about how much I think, cry because I think, and break because I can't seem to think in the right rhythm that would get me good grades.  I just kind of wonder why God made me think in a different way.  I think in a weird way.  I feel so alone and so angry.  I'm so stressed out, and tired.  I'm always so tired.  I'm so sad all the time.  I'm almost always an afterthought of everyone around me.  I hate it.  And, now just siting here on my bed, my head, oh, my head, it's spinning, it's pinning me against a wall, useless and hopeless and scared.  And now I don't see much reason for living.  All that matters at this age is being good, getting good grades, and being happy.  But maybe tomorrow be different.  Instead of choosing the end, I think I'll choose tomorrow.  The end ends everything, tomorrow can change anything.  So I guess I'll check in soon.  Bye.
XOXOXO
-Morgan