College is causing me depression, what can i do so i am not getting depressed/insane from school?

so i am taking some tough chemistry and biology cles this semester, and i feel INSANE, i am snappy at people, i can't handle stress, i want to break down, i feel worthless and miserable, i feel dumb when i don't understand something in cl. the school is causing me lots of stress , anxiety and i am depressed. what can i do so i can actually enjoy myself in these cles, instead of freaking out and getting depressed?