How can i run a mile quickly?

im 14 and at school on mondays we run a mile. (its a lacrosse cl) my first time i ran 9:05 last week i ran five seconds better every time i finish i feel like i could have done better it fells like a rib is in my lung im 123 pounds so i think i should be running faster but i get so exuasted it feels like i cant run anymore does anyone have any tips on how i could run my mile faster?