How do i heal myself and free myself from my thoughts?

i feel depressed i cant c anythinng good. i used to be stronger and would ignore everything that made me feel down. now i got weeker, i cant get over things. the top part of my left arm (not the same side asure palm) has a big cut on it that i did to myself to stop me from hurting someone else. i cut my nuckles up to remind me not to hurt anyone. i gaveup on god a long time ago. my usual thoughts are "**** it, were all going to hell anyways" and "i am ready for hell so why am i still here?" i have not tried killing myself because i feel that death is too good for me and i deserve to suffer. i hate that i feel like this because im a 16-year old guy. what is wrong with me? how do i make this better?