Don't know what is wrong with me

HI, so I'll just give a little background info before everything turned for the worse. I used to be a person with a pep to his step. I was filled with confidence, I had no doubt in my abilities at all. In a sense, I was cocky and full of myself actually. I am also a very, very hard worker... but it is also what i believe is contributing to some of my problems now.

This may sound weird, but it all got worse when I did not do well on my SAT...I worked so hard to achieve the score i wanted. I did a practice test every saturday for 2 months... i worked and practiced 7 days a week for countless hours. I expected the score i wanted and i did not get it. I was really devastated by that. My confidence plummeted after that. I haven't felt like myself since before receiving my score back in november of last year.

During the course, i messed up a relationship with someone that meant a lot to me... and i dont blame this person for wanting to do that because i understand what i did was immature... but i cannot forgive myself still. i think about it everyday.

i have felt unwanted as well. I am alone a lot now. I don't reach out to people much.. it is so hard for me to say my feelings really. Every little thing gets to me now... i used to not let anything get to me. I brushed negative things off easily. Idk, ive realized i dont have many friends... i always have to reach out to them just to have a conversation.

Mood: my mood changes a lot. i can be happy one second and then angry or sad the other. it has come to the point where i cannot expect having good days because i know my mood will change everyday because of something.

Self harm: I think about hurting myself but i never act on it because i know that is not smart but it doesnt stop me from thinking about it.

Anger: When i get angry, which happens before i get sad usually, i tend to hit and throw things and talk negatively to myself out loud.

*i used to see my school therapist and i am reconsidering talking with her again

I just wanted opinions if anyone know what is going on with me? is it something serious? or am i just going through some kind of a "phase?"