Need to get off my chest

I don’t know if i’m going to make it past 18, i barely made it to 16. Yet i’m barely managing as it is, during summer where i have no excess stress from school. I don’t think i’m able for life itself, if i’ve struggled this much for years of my life, starting from primary school all the way to now, entering 5th year, I don’t think ill make it to my grad. Being realistic I struggle with suicidal thoughts daily, i’ve made plans time and time again, only for something to interrupt my plan and me not going through with it. And despite still being here, not only are suicidal ideals a daily occurrence, thoughts of self-harm are so regular to my mind that i just don’t react internally to them anymore. Ive been told time and time again by my therapist that she believes there to be nothing more wrong with me than my already diagnosed anxiety and social anxiety, but i refuse to believe that there isn’t something more. The way I feel is so up and down and unpredictable for everyone including myself, one day i could be bursting with joy always smiling and laughing, yet the next i could be like a zombie, unable to move myself from my lying position in bed, according to my mother who tries to get me to move on those mornings, i’m “like a zombie”. I don’t react or reply to anything or if i do reply it’s not words, it’s simply a “mm” or “mmhm”. But I cant go on like this, if there truly is nothing else wrong with me mentally then how am i meant to get through my leaving cert and college if i’m already struggling with my mental health this much daily and i’m only finished TY. Please someone help me find an answer. I cant hang on like this, clinging to the hope that someday ill simply be told that they finally found something.