First of all, a valium overdose does not guarantee death. Vomiting is likely to occur and so you wouldn't die. It could put you in a coma though. That wouldn't be much fun.
There are other, more simple ways to kill yourself and you do not need a prescription to do it. But do you really want to kill yourself?
I understand your fear and trepidation of the place you find yourself in. I also understand that in order to get relief, you must be more creative than just deciding to kill yourself. Do you really want to end your life? Or do you want to end the problems going on in your life?
Here is the simple truth, as truth is often simple: The only way out of your situation is to leave.
There is nothing stopping you. Don't argue, please. Think about it. THERE IS NOTHING TO STOP YOU FROM LEAVING.
So what if you are shunned? So what if you are disfellowshipped? So what if you are disowned? Better that than to kill yourself or waste your life being miserable.
Think about each of your fears and tell yourself what is the worst that can happen? If you look deep within yourself, you will see that you can survive whatever may come your way.
Think about it, build up your confidence, and then take that first step to freedom. Then take another one, then another one.
No man made organization can give you salvation. And maybe, just maybe, God isn't this invisible, terrifying thing that will dash your brains out at Armageddon. Maybe God gave you your life to live and enjoy. Maybe you can worship him better on your own--without others telling you how to think, feel, live.
I took that leap of faith and just left. Yes, there were repercussions. Yes, I had difficulty. But I promise you that the joy, happiness and freedom are very spiritually uplifting.
Yes, it is difficult and frightening. It will probably be one of the scariest situations you will ever find yourself in. But you must do it.
Better to leave than die by your own hand.