How To Treat Hot Ankles After An Injury?

I have an 11 year old son who twisted his ankle Saturday. I took him to his doctor for an x-ray. The doctor said he didn't see a fracture. He told us to keep his foot elevated and ice it. My son just woke up crying in pain and his ankle feels hot to the touch, almost feverish. But the rest of his foot feels ice cold. What should I do?