Why am I grasping at straws in everything I do?

Hi all, sorry for self-pitying post title. 19m here genuinely convinced that nothing I've done/will do ever amounts to anything- academics, relationships, sports, whatever I do I am pushed to my absolute limits and still almost little to nothing is produced each and everytime. I feel like I work pretty hard, am more disciplined than the people around me (which doesnt necessitate a gold medal by any means), but am sill constantly just scratching the surface of average.

I go to a mediocre school (grateful to be enrolled at all, but constantly reminded I am a piece of shit for going here) have mediocre grades etc you get the jist. It is nearly impossible for me to get into research, summer internships, or anything of the sorts. I know comparison is the thief of joy, but I don't have any good role models in my life either so theres not much else to work with.

I feel like a loser 24/7, but not in a "I need comforting" way but rather "I need to change something and I'm willing to make any change necessary" i just dont know what that something is.

Anyone have any ideas as to what that something is? As the overly explained text above suggests, i am desperate.