Sounds to me like your boy may have stepped or jumped wrong and twisted that leg. Of course, without being able to see the dog in person and take an x-ray, it's pretty much impossible to tell if it's a simple sprain or something more serious. In cases of leg injuries in dogs, especially hunting breeds, I always recommend seeing your regular vet just to be on the safe side.
That being said, until you can get him in to see a vet, I suggest doing your best to keep him quiet. No running around, outside on a leash to go potty and then back inside. If he's used to being in a kennel/crate, you can keep him in there in an effort to keep him from jumping up on couches or running up and down stairs.
If he seems especially painful, you can give one low dose or child's aspirin, but make sure you give it with some food to avoid stomach upset, and do not give more than one every 8-12 hours and do not give it for longer than 3 days.
If the leg still seems to get more painful, becomes more swollen or if he is unable to bear weight on it, I suggest calling your vet or taking a trip the the nearest emergency vet and having them take a peek at it, just to rule out anything more serious than just a little sprain.
I hope this helps