Well firstly, I'm sorry to hear of what you've been through and congratulations on overcoming your obstacles.
Can I assume (or if not, suggest) that you want to reflect the transition in your life from the past to the present, the negative to the positive, as opposed to reflecting the actual hardships themselves? So that you can look on the tattoo as a positive symbol of who you are now, as opposed to a reminder of what you've been through in the past?
Well, to start with traditional symbols. The most obvious thing that jumps to mind with things like this is the phoenix. Obviously a symbol of rebirth, new beginnings, etc. It's been done a lot but that shouldn't matter too much to you, and the bonus of that idea is that, being a mythological being, the design is totally open to your interpretation, and you can design (or have it designed) totally unique to yourself.
Or you could go down the Japanese themed line and have, for example, a tiger, which is a symbol of strength (traditionally physical strength but can be applied to inner) perhaps with some traditional Japanese black waves in the background and some cherry blossom, which to the Japanese represents transcience of life, which isn't entirely what you're looking for I know, but it can also be applied to the fact that suffering is only short lived and transitory. And, although it's mixing cultures a bit, cherry blossom to the Chinese represents power and feminine dominance.
Another 'traditional symbol' idea is the swallow, which are typically nautical tattoos - sailors had them to represent 5000 miles travelled at sea, as swallows would fly great distances but would hop on board boats that were nearing land and show sailors that they were close to home. Which could, in a way, be metaphorically applied to your life - you've been on a long journey but now you're nearly there.
You could also consider a quote of some sort. Here are a couple of pages with some ideas:
http://thinkexist.com/quotations/overcoming/
http://quotations.about.com/cs/inspirationquotes/a/OvercomingAd1.htm
That's the traditional ideas that I can think of out the way. But just consider this - you don't have to find a traditionally recognized symbol for overcoming obstacles, something that someone else, somewhere along the line, has decided 'this is what it means'. You can create your own meaning behind anything, it doesn't have to be an obvious motif. Is there something you find particularly beautiful? Something you've always loved? If there is, you can have that tattooed and it will still be a landmark in your life. You will always look at the tattoo and remember the reasons you got it and the point in your life at which you had it. Do you see what I mean? Anything can have a story behind it, even if it's not something you can find on a search engine by looking up symbols. But if something traditionally symbolic is the road you want to go down then that's absolutely fine - just putting the other idea on the table!
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Just wanted to add, in reference to Pam B's answer, I don't know if she was speaking about what I said or not... but I absolutely wasn't putting the idea of anything down, I don't want it to sound like that. I don't really like to refer to my own issues in my past when we're focussing on you here, but all I can say is that this is the angle I would personally come at it from, and I am in a position to be able to say that, I'm not just speculating on how I think I might feel. Personally, when I see reminders of negative aspects of my past, it fills me with bad feelings. I can't derive a positive from that. But of course it's an entirely personal issue, and I really hope it didn't come across as me saying "You should do this or that" - perhaps I was wrong to allow my personal viewpoint to cloud my answer so much as we're all so different, but I was just giving you my personal opinion. I'm not putting down that type of tattoo at all, and at no point did I say I was.