What Causes Itchy, Red And Painful Lump On Knee Cap?

Hell DR. I am only a child - and at school today I received a mosquito bite right under my knee cap. It was a little bump at first, but now I notice its a hard, warm, large lump. It feels as if a new bone grew there. It is sometimes itchy, i can maintain the pain though -- since i have 5 other bites. Do you know what this cause is? Thank you!
P.S -- I only itched it a little bit but that was when i first started noticing it and I didn't know what it is. Also, it's quite red.