Hi Francesca
It sounds like you have been a though a lot over the last year and the bullying you experienced has stayed with you. When someone goes through a difficult time it can sometimes be hard to get over what has happened.
You mentioned that you had spoken to a counsellor at ChildLine but you still feel the same, sometimes it can take a few conversations with us before you start to feel differently. Often people who have been physically and emotionally bullied have issues with their confidence which can take a while to build back up. Writing down what you want to say to the teacher might be an easier for you to tell them about your problems.
It can be hard to hear people laughing at things we do but people have different ways of coping and it sounds like you use self harm to cope with how you are feeling. There are different things you could try that may give you the same feeling as self harming. Some people find pinging an elastic band on their wrist or holding an ice cube in their closed hand gives them the same feeling as self harming but in a safer way.
You might find it useful to look around the ChildLine website, there is lots of information and advice in the Explore pages about bullying. There are also the message boards where you can talk to other children that may have experienced bullying.
Take care
Sam