What Causes Swelling And Pain In Ankle After An Injury?

I work as a CNA, and when i was in a resadents room i twisted my ankle at an odd angle and herd a kind of craking popping sound when I did this. there has been some brusing and a lot of swelling. I can stand on it and walk just fine with minamul pain, but when I got up this morning I couldnt stand on my foot at all. Do you have an idea whats wrong?