Guys, I cannot thank you enough. You don't know how much it means to me that there are people out there who understand.
In response to Crimson Black, I'm 18. Yes, it's true that I'm not always confident and happy when I'm putting on a face of being confident and happy, but I really feel as if no one I know would understand. Some of them have their problems, depression, anxiety, but if I told them how I feel, they'd think I was doing it for attention or something...because I've got nothing in my life to feel unhappy about. Loving family, good grades, trusted by teachers etc. So why do I loathe myself? No one would understand.
In response to blackswan, it helped a bit. It felt as if all my insecurities, all my hatred of myself, all my painful memories and unhappy experiences, just disappeared for a while, and I didn't think about anything - there was nothing in my mind. But then I felt incredibly embarrassed and ashamed that I did that to myself, so I suppose it's just added to my hate of myself.
Sorry for the outpouring...I just feel as if I have to say it to somebody, some people who understand. Thank you all again so much for your replies, it's really helped a lot.