Karma is very, very real. You get what you give. What you send out, emotionally, physically, spiritually, whatever, WILL come back to you. I don't know if I really believe in the three fold law or not, but I admit it's definitely plausible. I don't believe that it means you'll get what you give times three. I believe that it means you will get what you send out on the three levels it affects: physically, spiritually, and mentally/emotionally.
Have you ever thought, "Why me? WHY is this happening to ME?!" Well, I'll tell you why. Life is a bitch. No one dies a virgin because life screws us all. Bad things happen to good people everyday. But that's a good thing, in some ways. Think about it this way: Would you REALLY enjoy the amazingly good moments of your life if you hadn't ever experienced a bad time? I doubt it. Another possible culprit for "suffering?" Karma. Think about all the times that you've been in a really crappy mood and lashed out at other people, or just generally sent out negative energy in a bad way (I'm not talking about meditating or something to chill until all those bad feelings are gone, I'm talking about just being generally pissed off and not doing anything good about it). Maybe when something negative comes back to you it's karma's way of returning to sender.
I have lost count of the number of times that I've genuinely thought that I hated my life and wanted to die. I'm bipolar, and I've been suicidal and would have killed myself if someone hadn't intervened. I was also a cutter for about 11 or 12 years. I started young (when I was about 9 or 10). Lately, I've thought a LOT about my life. Maybe it's because I'm revamping my BOS or something, I'm not sure. But I've been spending a lot of time thinking about me and my life and I've learned some things. Since I started paying attention to my thoughts and making an effort to be positive as often as possible, and release my negative emotions in a good way (such as through journaling, meditation, turning on Family Guy and grabbing a beer while surfing the net, etc.), my life has been lighter. It literally feels like this huge weight has lifted from my life.
If I could only give you ONE piece of advice for your life, it would be to make yourself think positively as often as you can. Try affirmations, they have really helped me and I've seen amazing results (maybe I'll post a blog about my first REAL attempt at affirmations, later). The power of your mind, your thoughts, your emotions is astounding. You will not believe the changes you'll see in yourself until you experience it. I know I didn't.