Self-Injury Support Group
Whether you or someone you know or love struggles with self-injury, this is the community to discuss your experience, find support, meet others going through the same, and get advice on how to stop. Working together, we can help find alternative coping skills to reduce the urge to self-harm.

Having said that bring a knife to school was pretty lame move....you knew that would get you in trouble and yes they can suspend you.
If your parents want they can put you in the hospital to get you some help but the school can't force you to go inpatient.
Your young and you need to stop this NOW before you get seriously hard into it. Thing being an alcoholic and a drug addict at the same time, now think harder than that.....that's what cutting and self injury does to you, it grabs you by your soul and it makes it almost impossible to stop...this is not a battle you want to fight.
Self Injury is a "learned behavior" which means you can replace it with other safer healthier learned behaviors. You can learn coping skills that help you treat yourself better when things are stressed and hard and emotional and scary. You need to talk to your parents and tell them you need to see a Pdoc (Psychiatrist) that's where you'll get the help you need.
You don't want to be here 35 years later trying to figure out how not to cut. I had a very bad weekend, a friend of mine was killed and in a rage of anger/pain/loss/grief I screwed up and cut my arms up. I had to go to the ER and get stitches.
Then the got infected, so I had to take antibiotics. I've been to the ER 3 times in 5 days, 2 antibiotics later and in the morning I get to go back to the ER and get the stitches out, get the infected tissue cut out, get IV antibiotics and have everything re-stitched.
This is not a fun life and it's not a life you want to get locked into.
Have your folks take you to a Pdoc and get some help.