Am I fainting due to my knee. Help... URGENT!!!!?

I have had an on going problem with my knee where it keeps clicking and aches all of the time and hurts a lot when I excersise. Sometimes after excersise it swells up and is very bruised. In the past week, whenever I run or climb up or down lots of steps or nearly anything puting pressure on my knees I faint.

I have not been diagnosed with anything for my knees or fainting yet

I am I fourteen year old girl and am very active and sporty. I am average weight and very healthy.

There is no history of fainting or knee problems in my family.

When I excersise I drink lots of water, est healthy and enough, don't skip meals and have plenty of sugar.