Hi there. My name is ***** ***** I"m happy to help you with your question.
Sounds to me like your pup may have injured himself playing with the new puppy. 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 injuries in dogs, especially tenacious breeds and/or toy 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, no dog park, just 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 or rough housing with the puppy.
If he seems especially painful, you can give one half of a 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 2 days.
If she seems to get more painful, becomes swollen anywhere or if he is unable to move around , 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