Please talk to a health professional. If you can't do that initially then find a friend or family member to talk to. These people can be great for support, but you ultimately need to talk to a professional.
I have dealt with my own acute depression. I know that sometimes there are reasons and pressures that pull us down, and other times it just happens for seemingly no reason at all.
I am happy to listen if you want to chat more, but really, my only advice is to talk to a professional. Please.