Possible skin cancer?

I've had this mole for about four years now. It's right on my back where I don't see it often enough to know what it really looked like when I first got it..but it's become tender, and the color looks different on one side, as well as the shape. I'm only 23, but I did live in the philippines, hawaii, and california when I was younger with little sun protection. I have a doctors appointment set up for a week out, but I was wondering if anyone had any opinions.