Depression: is it a sign?
I just wanted to mention something that's been playing on my mind a lot lately and may apply in your situation as well.
You asked about anti-depressants, which may, or may not, be right for you. That's a decision you and your doctor will have to make together.
As for therapy, however, there are 2 things I wanted to mention: the first thing is that you can ask about group therapy. You didn't mention where you live, but in most large cities your doctor or therapist can find a group that is specifically for teens. Make sure that you try and get into one of these groups, because you won't have a lot in common with a group of depressed 40 year-olds, and then you may not feel your issues are valid.
The second thing I wanted to mention is that there's a need for therapy in situations like yours. You were exposed to some pretty bad life lessons at a young age. These experiences have helped make you who you are today, and who you will be tomorrow. The question is, how "normal" will you be, if your thought process is, um, skewed, or "off-kilter", due to these experiences? A therapist may help you change while you still can, and help you avoid self-inflicted emotional pain when you are older.
From your posts here, you sound like a very intelligent person who is self-aware enough to know that it's time for help. Believe me, these are qualities that will work for you. Nurture them, and stay strong.
Keep us posted about your decisions, please!
The road to recovery begins with the assumption that you have a right to be you. It ends when you realize that you want to be.