It really hurts and mum and dad don't believee me?

ok i am 14 and quite sporty and i have always been but for the last year my knees have cased me ALLOT of pain i cant even run 100 Meters any more and when they do start to hurt its like a poking in the sides of my knees and then if i try to carry on it gets to be like a stabbing in both sides some tines its worse them others and somethings its just there and i can wake up with it in the morning. but if i like fall over then it can b like really pain pull for like a week. i have try freeze spray and pain killers but it dint help and my mum nd dad dint believe that they actually hurt me what should i do