Help please i have really hurt my knee!?!?

Okay so when i was at school i tripped up the stairs on my way to lesson (concrete ones) and landed on my knee. then about a week later my dog tripped me up and i fell on the floor and landed awkwardly on my back and hurt my knee again. then a couple of days ago i fell into a hard wooden chester draws and hurt the same knee AGAIN . then today i swung my legs under my desk (in textiles) and i smashed it again. please help im in loads of pain .. any answers would be greatly appreciated .x.