Hi Soda, thanks for sharing this! Unfortunately, this is true for a lot of us. We tell others not to do the very thing we do ourselves. I understand having to find a quieter, subtle way to let out your emotions. You can't throw a tantrum at 19, people would call the police or you'd get sectioned; so the only alternate in letting out that pent-up energy is by self-harming.
Are there any gyms nearby that you can take up classes to let out this anguish? I would suggest looking into that, and with New Year's so close and all those ridiculous discounts popping up, I would take advantage! See what classes they offer, such as kickboxing or boxing that requires the use of your limbs. Or, alternatively, I would suggest signing up for a sports league in your town, ask people you might have connections with if they can get you in. For me, soccer is a great way to let out that energy although they're not the limbs I want to be using — ie, in the context of self harm — but they still exert energy.
Also, you are great with words! I remember you used to write in the Self-Expression form. Although it might be considered a 'passive' activity, I would suggest taking the time when you can and write. Just write what's on your mind and you certainly don't have to share them with us. Keep them for your eyes only. If you feel comfortable, then go ahead and pick a piece to share with us whether that's in Self-Expression or your user blog.
Whatever you choose to do, I hope you continue to take care of yourself. All the good thoughts and vibes your way.