Cold, numb, sore foot?

So for the past two weeks or so I have had on and off pain in my right foot/ankle. Sometimes it is perfectly fine, other times the pain is unbearable and I am hopping. Usually it is just an annoying ache in my ankle when I walk. I haven't noticed any swelling or anything, but i'm 13. What could be wrong with it and how should I treat it (I play a tonne of sport - tennis, swimming, running, dancing, gymnastics - so I hate injuries)