Talk to someone tonight - ring a hospital, ask if they have someone or can put you on to someone who you can talk to tonight. You've got nothing to lose by doing that.
I've been in your position, I know how hard it is waiting to feel better. Anti-depressants take up to 4 weeks to really take effect. Self-mutilation and testing how much medication your body can handle won't help. Write down your thoughts, get them on paper out of your head. Talk to a professional. There is hope, believe me.