Sounds like a bad sprain. Is he using it all (putting it down for balance etc). Is it just pink and swollen or does it have blue/purple streaks? Pink and swollen is more likely to be a bad sprain, streaks could mean a fracture. You can give infant liquid ibuprofen every 4-6 hours to help with pain/swelling, but just for a couple of days until swelling decreases. Any idea how much Stewart weighs?