toddler fell and hurt his ankle?

My almost 3yr old son went swimming and fell out of the pool and hit his right ankle on the cement. His ankle is swollen and the cement cut his ankle and foot. So I took him to the e.r. and they did x-rays and they came back nothing is wrong with it. The film showed no break, not bruise, no swelling, no nothing. But he is complaining that it hurts him and he is limping on it. His ankle looks swollen and puffy to me. I feel something is wrong with his ankle. My son is not a complainer so that worries me. When he moves it he yells or if we try to look at it, he yanks his foot back like it hurts..... this just happened tonight. Should I listen to the x-ray when it says nothing is wrong, or should I listen to my motherly instincts and get a second opinion?? What would you do?