I wish my leg wasn’t hurt

Ïn all honesty I enjoy sports [sometimes.] like soccer basketball dancing [yes dancing js a form of sport….i tjink] and turns out Ïm super good at baseball and basketball [even though I mainly like soccer and archery] only problem is, MY LEG!!!!! My leg has somthing wrong with it ï don’t exactly know what…but it’s somthing! If I run for to long stand walk jump anything active my left leg right below my knee starts to feel SO MUCH PAIN. Like a thousand knifes stabbing me at once!!! Sometimes I even collapse because my leg CSNT hold myself up anymore