I need help determining what is wrong with me.?

I am a 21 year old female. I always feel shaky, i get muscles spasms, dizzy spells, i feel nautious every once in a while, muscle pain, chest pain, black stool, irregular period and when i do get it its extremely light, my hair is thinning as well, and im always tired but cant seem to sleep. I AM NOT PREGNANT. i know that for a fact. Could it possibly be my thyroid? I really need help figuring out whats wrong with me. Im going to go see a doctor but i like to know or have some idea what im in for.