You need to get this checked asap, it is definitely a mental illness of some kind, from what you described there are some symptoms of depression there but the thoughts of harming others sounds like a different type of diagnosis altogether. If you really are worried about someday losing your cool and doing something to harm someone you need to get checked out sooner rather than later.
I don't really feel like I can talk to my mum or dad or my twin brother I just think they won't take it seriously
Teen aged years have got to be the hardest for all of us. Fortunately, people are more apt to accept treatment as an option these days for some of the things that you're describing. Are you able to talk to your mom or dad, or both about how you're feeling. and let them know that you think you need therapy? and that you'd be willing to go? Because i really, really think you need it dear. Might as well get working on this, it's not going to go away by itself i don't think. Is there trouble at home (that could be the cause of your anger)?
Thanks for posting here.. I appreciate your honesty and bravery for doing so.
I am also self harming when something stresses me by cutting my leg I have also tried to brake my foot with a weight and have taken and overdose of paramax tablets. I also think I have social anxiety as I really hate confrontation and if someone watches what I am doing I get really nervous I hate talking to new people as I find it difficult to speak and I hate when I have a family get together I feel really worried that I will make a foul of my self
Do you have insurance or a way to see a therapist?
Can you go to a hospital, and try to talk to someone in the Psychiatric Ward. It might just be a chemical unbalance, something that can be managed.
Before you do something stupid, go to one of the prison sites and write a convict and ask what it's like to be locked up 24/7 for the rest of your life, with prison gangs beating you up for your desert and commissary, no rights, sexual assaults, nobody to go to, no air-conditioning, limited toilet paper, constant noise, rancid bologna for lunch, mail censored, and getting locked in the hole on bread loaf for a month for making a complaint.