X3, I am sooooo glad you have gotten on this forum. You do need a safe place to talk about
this. One of the important things you can do is track your moods. So get a notebook and divide the days into morning, afternoon, evening (but if that is too much just track for a full day and don't divide it). Then make a very brief note of your mood for the different times during the day or for the whole day - even a thumbs up or thumbs down symbol. The goal is to be looking for patterns - like the evening being harder, or a series of days being harder than other days. If you can note triggers to mood shifts, that would be a big help - like when a friend speaks to you a certain way, etc. Trying to make sense of our mood shifts sometimes helps in being able to control them better.
I still wonder if it would not be good to go to your school nurse and speak to her and ask for her advice. You can explain to her your predicament. Just say you have a headached and ask to go see her. Are you scared of your mother finding out you have talked with her? What would your mother do?