Hello again Demetra and thanks for waiting.
Sorry to hear about Sammy's problem, however I have worked out an answer for you, please read it through and see what you think ...
1. Well it could be that what you are seeing is related to pain from some kind of soft tissue injury such as a strain or sprain but it is also possible that Sammy is in the grip of some form of infection or other. So difficult to differentiate over the internet ...
2. Antibiotics or other prescription drugs could be what is needed if your dog is indeed in the grip of an infection, but as I say other diagnosis are also possible.
3. Given the above what you should do, just to be on the safe side is have a vet check Sammy over sooner rather than later. In the meantime all you can do is to keep him comfortable and reassured.
4. I have known owners give aspirin to dogs while waiting for their vet's appointment when they suspect soft tissue injuries and report success. On a short term home remedy aspirin would be much safer and more effective than the other over the counter human pain killers and aspirin is sometimes prescribed for dogs.
A typical dose rate would be 5 mg per pound of your dog's body weight twice daily. The judgment whether to dose with aspirin is of course up to you but here is a link to a an accurate web page with all the facts you might need including contraindications : LINK
I hope I have covered your question fully enough but if you would like further clarification or to talk things over a bit more then I will be on-line for the next hour or so and I will be more than pleased to continue working with you.