I don’t know where to put this but..:

I don’t know why but for the last month or two I’ve been feeling constantly sad or angry and if I was happy the next second I’d start crying for no reason. I’ve been getting really angry for the slightest things, eg. in volleyball in pe I would miss the ball because I wasn’t able to jump high enough and I would dig my long nails into my skin almost to the point of drawing blood because I was so mad, other times I would walk off after and punch a wall. I don’t know why I’ve been acting like this... any advice or something?