Vet could of course be wrong with initial assessment but usually they can tell if infection present. Here is a list of possibles to check out if x-ray reading negative:
https://www.google.com/search?q=swol...hrome&ie=UTF-8
Licking paws often? Is he holding his front paw up, bearing weight, limping, lying around or restless, nervous, breathing normally, changes in eating, drinking, eyes squinty, runny or normal, abnormal poops & pees, nose dry, runny or any other symptoms?