Sorry to hear that your sister bullied you like that, I had similar experiences growing up. I also had a phase of being a bit overweight as well, people can be jerks and I include myself there because when I was a kid I had a phase of being a jerk myself, though I feel like I do a lot better these days and I'm glad I grew out of that phase within a few years for the most part!
And yeah, I try to forgive everyone... Though, I can't really forget and I'm not sure that would be a good idea even if I could.