I just read this now. I've just finished reading a fantastic book which has really changed the way that I think. It's called The Law of Attraction by Esther Hicks. I borrowed it from my yoga library and have since bought it online. Basically, it says that what you think about, you attract (the good stuff and the stuff that you don't want in your life, but also focus on or fear, the more you think about it, the more you bring that stuff in). I only mention it b/c you said that you tend to try and think positive etc and this book was along those lines. The book was saying that most of us are not aware of directly creating what we want in our life (and/or fear or doubt gets in the way, instead of allowing things in etc). We can't change other people or what they attract to their lives and we can't change what happens to others (illness) or how they behave.
I don't believe in curses, other than the power of belief that people attach to them.