A very good start — and I think the right place to begin. You are showing a tremendous amount of courage by explaining yourself here. You also show good insight by linking your bad moods and tiredness to the self-harm. Sometimes, when there is a lot of pain inside, the self-harm moves it to the outside so it can be seen.
I can understand you may not want to tell your friends or a teacher or your parents. But telling a physician would be the next step after writing us here. First of all, the physician can check out the cuts and bruises to make sure they are healing properly. This is when you can talk to him or her and ask what the next thing to do is. Telling a medical professional who has had training in how to help is the best thing you can do for yourself right now. It is time to be brave and continue what you’ve started here.