Cutting can be a very complicated desire. The wrist is a dangerous place. You are 13 and in a difficult time period of life. The teen years always seem to be a hard time to deal with. You can be helped and you need to get it as soon as possible. You could accidently cut enough that you end your life. Yes, your mom would get upset, she loves you.
From ones that I know that cut, it seems to relieve them by letting out what causes the depression, or so they can see their pain. Scarring is going to stay. You are at an age that many young people cut. They get stressed dealing with things that are happening and up and down hormones. You are wise to ask for advice on this.
If you don't want to go to your counselor at school, you can call the Mental Help Services in your county or city. They also have a hot line available that can lead you in the right direction, and be there for a crisis time. Get in contact with a source that is available to you to get help now. Don't let this go on any longer before you seek help. The earlier you get help, the more it will help you. Don't feel that you are different or look down on yourself because of it. You are not alone in this. There are many that deal with this situation, be it young or older. RJ
It can be related to bipolar disorder but only a psychiatrist could provide an exact diagnosis. Bipolar disorder is very treatable. If you feel uncomfortable speaking to your mother about it you should speak to a school counselor and they could help provide you with a referral to a psychiatrist if that was needed but in addition to medication talk therapy can be helpful as well.