Idk whats wrong! is my leg ok?

This morning in gym a few people had to run an indoor mile. i was one of them. i was the first to finish and when i got done my leg hurt right when i stop running. im not a big fan of running but i run a lot. i couldn't even walk on my leg it hurt so much. at about 2:00 i bent down to pick something up at school and after that i sat on the floor and my leg started to feel tight around the kneecap. im really scared because i play a lot of sports. and before 2:00 i couldn't even put my leg out straight it hurts still and idk what to do.