How to ask for help

I know something is wrong with my mood but i dont know who to tell. Most days i cry, am excessively tired, have a hard time focusing, or have a lack interest in anything. It started middle of junior year (high school) and im now a senior so its been going on for almost a year. I used to be an A student but my grades dropped. I stopped caring about anything. I self harmed at the end of junior year because i just felt useless and i did stop that. Recently, i went about a week without talking. Social interactions are tedious and exhausting. I really dont know what to do. My friends at schools are very fake and not the nicest and when they confronted me about how i was 'acting' they said i was neglecting them and being a bad friend. They are just not good people and are really not helping the situation. Little do they know, i cant help the way im feeling. Please give some me spme advice, i think i need it